Chapter 3:The 8051 Micro-controller based computer system
Contents
1. Erecise3 3 Guess what are ACC SP in the above table Exercise3 4 What assembly instruction should you use to access the value of IP Exercise3 5 What assembly instruction should you use to access the value _ of external RAM location 2345H Exercise3 6 Under what circumstances should program memory location 9256H be accessed Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a 3 6 Assembly language of the 8051 Learn this from the textbook you brought 3 7 A simple 8051 Single Board Computer SBC design Now let us look at a simple computer based on an 8752 UV EPROM based 8052 micro controller device Ft Pt het et bt bet bt tt SS See Sees eos APALGHES E LEDHP L 2 22 22 Sree AFPALGHHS K DDDDDDDDDDDDD Hrer GON ee ee Peo ZNONTNHd M 2529 a EERE Pd hd Pt bt ht ht ht ADDRESS Figure 3 4 An 8752 based microcomputer from 8 This is a small Single Board Computer SBC system with the following hardware modules One 8K data RAM 6264 one 4 K program ROM inside the 8752 A simple resistor capacitor RC circuit to pull down the reset pin pin 9 after power up A Crystal of 11 0592MHZ is connected to pin 18 19 d Serial interfaces MAX232 RS232 to TTL level interface at pin 10 11 Note that RS232 uses 12V and 12V to represent low and high while TTL uses 0 and 5V to represent low and high respectively First let us look at what the 802. gt gt Has an 8031 micro controller Power management circuitry to cope with power down failure One 8 32 Kbyte 6764 or 67256 startup ROM One data 32 Kbyte SRAM 62256 One 32 Kbyte data program SRAM actually 24K is usable Two 8255 parallel interface chips totally 48 IO bits One real time clock DC1287 with internal battery for keeping system time and generation of interrupt clock RS232 interface to PC through a converter chip MAX 2372 Watch dog timer MAX691 A full bridge rectifier circuit and a power stabilizer 7805 for accepting 7 9V AC or DC power supply LCD interface to a standard 20x2 LCD panel 3 9 1 8051 and external memory interfaces We will first start to discuss the interface between the program Rom and the data RAM Then we will talk about how to make RAM used as both program and data store Recall again the 8031 has three external memory read write operations Table 3 2 8051 external memory read write operations PSEN RD WR 1 External program read O 1 1 2 External data read 1 0 1 3 External data write 1 1 0 3 9 2 8051 and external program ROM UV EPROM interface Our system uses a UV EPROM or called EPROM US in the 8031RL schematic as the read only memory store to hold the startup program The circuit is a straightforward one and requires the 74373 to latch the address and the ALE of 8031 is connected to latch input LE of 74373 The system uses a program
3. a13 WR a12 RD Atty 410 as 48 eo nNwur Figure 3 1 This is the 8051 pin assignment diagram from 1 Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a 3 3 The 8051 micro controller family All have 128 bytes internal RAM 2 timers 32 bit parallel IO serial IO 5 interrupt sources 8031 ROM less use external ROM for programs 8051 4K byte ROM 8751 4K byte UV EPROM ultra violet erasable re programmable e 8951 4K byte 7 Flash ROM based Electrical erasable re programmable o Philips extended Architecture 16 bit with AD converter 8X52 An extended member which has 256 bytes internal RAM and 3 timers Exercise3 2 Search another 8 bit MCU e g MC68HC11 or Z84 on the _ Internet discuss and compare it with the 8051 in terms of a maximum i speed b memory size and c interrupt features 3 4 Fundamental operations of a micro controller based system A typical micro controller system has the following configuration Clock Micro controller RAM for data and oscillator e g 8051 program i e 11 0592 Reset Mhz switch m reset ROM for storing startup program Peripheral IO devices e g 8255 8253 real ND 2 time clock etc Figure 3 2 A typical micro controller system Every microprocessor system has a similar startup and operating procedure which is depicted below The microprocessor is connected to a clock whi
4. multiplexing of signals is used For example port 0 and p2 are used as input output ports or memory interface pins Here we will study the memory interface methods and see how they perform during memory read write The three topics that we will discuss and their related hardware pins are as follows 1 Address and data bus time multiplexing for external memory devices 2 External Program memory read Hardware pins involved port 0 and port 2 P0 1 P0 7 P2 1 P2 7 16 bits and ALE PSEN 3 External Data memory read write Hardware pins involved port 0 and port 2 P0 1 P0 7 P2 1 P2 7 16 bits and ALE PSEN RD WR 3 8 1 Address and data bus time multiplexing for external memory devices As discussed before an 8051 has 4K internal ROM to store programs But if we use the 8031 version or if you want to have a program longer than 8K we need to ask the 8031 to access external ROM Note that when pin31 external enable EA of an 8051 is grounded it will ignore the internal ROM and use the program from external ROM it will be treated exactly as an 8031 Alternatively if pin31 is connected to 5V the 8051 will read programs from the internal ROM Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a Let us examine the circuit diagram and see how a ROM memory chip is connected to the 8031 The ROM device is 270251 which is a 64K 2 bytes with 16 address pins ROM To save the number of pins we s
5. CS of RAM2 Data E000 E003H CS of 8255 U8 Data E800 E803H CS of 8255 U9 Data ECO0 ECOD CS of DS1287 real time clock Data F000 F002H CS of LCD Table 3 3 Input output peripheral devices address map 3 10 Conclusion The design and functioning of an 8031 single board computer are discussed in this note In particular basic knowledge of how to use the 8031 internal registers interfacing 16 Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a 17 techniques to external memory systems and parallel input output pins are given Various hardware development techniques are mentioned 3 11 References 1 MCS 51 Microcontroller Family User s Manual from page 1 50 http www intel com design mcs5 1 manuals 272383 htm Data sheet of a 32K byte Static RAM SRAM device 76C256 http www skt co kr gm76c256clcll pdf 8031 serial interface http www 8052 com 805 ser htm Manual 8031m7 pdf of 8031 RL SBC from http www cachecom com Philips MCU home page http www semiconductors com mcu http www cse cuhk edu hk khwong ceg3430 htm Useful information Amtel s 8951 page http www atmel com atmel products prod20 htm Paulmon http www pjrc com tech 8051 pm2_docs hardware html Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a 3 12 Appendix 1 Figure 3 13 Address map of the 8031RL SBC all addresses are in hex Exter
6. up program why does sp 30h 1 not 30h i What does tell you about the stack operation of the MCU e The 8051 has 128 bytes of internal RAM for storing working data such as the stack and variables But if that is too small for your program you can use the external data RAM 6264 attached 0000H FFFFH to the 8051 The assembly instruction for external RAM read write is movx Now it turns out it is not a single chip system after all A basic system would at least have a minimum set of electronic circuit For example a circuit to turn the action of pressing of a button into a Ims high pulse signal reset signal Also some circuits are needed to connect the 8051 to a ROM for storing program and RAM for storing data In fact if you use the 8051 version of the 8051 family it has a built in 4K ROM for storing start up and necessary programs or for the case of the 8951 which has 4K electrical programmable Flash ROM for program development purpose Exercise3 10 State the differences among 8031 8051 and 8951 Explain i how to enter a program to an 8951 Exercise3 11 The internal RAM has addresses 00 DFFH and the external i data RAM also has that same addresses will it create a conflict Answer in terms of hardware and software aspects 3 8 8051 memory interface Diagram from http www pjrc com tech 8051 pm2_docs hardware html The 8051 is designed for small systems in order to reduce the number of pins used time
7. v 4 a Figure 3 9 Software development using monitor ROM To have the above scheme we need two important things 1 A program at the ROM for monitoring the 8051 system it should be able to communicate with a host PC computer and download object file form the PC to local RAM and run the program there Thus this program at ROM is called a monitor program 2 A shared RAM space for holding program and data simultaneously in this light we have the design shown below Shared program and data extemal RAM 8031 TFFFH TFFFH RAM 62256 ROM 27256 0000H 0000H Extemal program Extemal data RAM ROM The 8031 SBC RAM and ROM The upper 32K RAM isshared between program and data Figure 3 10 Memory architecture showing external shared program and data RAM One way to have this development system is have a program ROM at 0000 7FFFH to store your monitor program a simple operating system data RAM at 0000 7FFFH for storing variables and your working data It is noted that even the address is the same as the program space it doesn t matter since program and data are separate entities and differentiable by the hardware signals PSEN for retrieving programs and RD WR for read write data reps The most important part is a program data shared RAM at 8000 FFFFH for storing data and at the same time for saving programs for testing It is interesting to see that this RAM space can be used for both purposes such that Itis trea
8. 000 7FFFH has A15 0 E WR WE of 8031 E OE RD of 8031 RAM2 8000 FFFFH program data shared a CE A15 for all addresses 8000 FFFFH has A15 1 E WR WE of 8031 E OE PSEN and RD either data read or program read will get output Decoder GAL 18CV8 Figure 3 11 Address decoder and memory devices Exercise3 14 Redesign the above circuit so that we only use address space _ 8000 DFFFH of SRAM2 1 In practice the operating system or monitor program will be in ROM1 The development cycle is 2 At power up it will enable a serial communication link with a terminal Windows Hyper terminal etc 3 A programmer will develop his program on the PC using a cross compiler of C and generates 8031 executable code object code 4 Then under the instruction of the developer using the monitor program it can delivery the object code to the space starting at 8000H as if it is writing data to this space 5 Finally the developer issues a run from 8000H command to the monitor program at the 8031 SBC and the 8031 will execute from that location which is the object code he she is testing The advantage of using this development system is e The development hardware is very minimal a single chip computer a PC and a serial cable no need for an In Circuit Emulator which is an expensive piece of equipment e Turn around time is fast there is no need to blow an EPROM may take 10 minutes or more for a developme
9. 51 system will do after reset e Power up or reset After power up or when the reset pin 9 is at high for about 1ms if the master clock is 1OMHz or over as discussed in the data book of 8752 the system is being reset Then the 8051 will fetch its first instruction from the ROM space at address OOOOH Special care must be taken when you write the first instruction Usually it is a long jump instruction to the system initialization such as setting up the system clock serial communication link with a host computer or loading the start up program from flash memory to RAM i e boot loader etc e A simple startup assembly segment is as follows 1 Org 0 OOOOH is the first instruction after reset 2 ljmp start long jump to the line labelled start line 6 3 Org 30h arbitrary but addr 0003H 002FH 5 are reserved for stack 6 start mov sp 30h 1 set stack point at 30h internal RAM max size 7 is 64 bytes 8 the stack will grow up to the max address of 7FH 9 Other start up program segment Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a Exercise3 7 The R C connected to the reset pin9 of the MCU is 4 7K and 10uF respectively explain the choice of these values Exercise3 8 Describe how to modify the hardware circuit to have a 32 i Kbyte RAM You should first determine the pin number s of the 32K RAM i and see how it is connected to the system Exercise3 9 In the above start
10. 8CV8 for address decode So that if necessary one can change the address map by changing the content of the GAL chip The connections are as follows gt A15 of the 8031 is connected to CE of the SRAM through a MAX691 watch dog timer chip Let s forget about the special functions of the MAX691 its function will be explained later and treat it as a direct connection Therefore whenever A15 0 the address is within 0000 7FFFH the memory chip is selected The read write operations are now coordinated by RD and WR of the 8031 gt RD pin17 of 8031 RW pin16 of 8031 are connected to RD pin 22 of 622256 and WR pin 27 of 62256 respectively Since during external program read as discussed above in Table 3 2 RD and WR are high therefore only external data read write instructions can read write this SRAM gt As a conclusion this SRAM will only used for external data storage 11 Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a 12 Figure 3 8 An 8031 and External Data SRAM 62256 interface Note that treat MAX691 as direct connection at this stage 0000 7FFFH external data RD WR select output Address A15 PSEN decoder RD WR 18CV8 ALE POO PO7 AOAT DO D7 Address dat multiplexed P20 P26 A8 A 14 RD WR 3 9 4 8051 and data program RAM interface Making the RAM as both data and program store Refer to the schematic of the 8031RL SBC fr
11. Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a Chapter 3 The 8051 Micro controller based computer system Objectives Study the structure of an 8051 micro controller based system Study the internal memory model of the 8051 Study the external memory interfacing architecture to enable on line software system development Study addressing methods for interfacing various input output peripheral devices of an 8051 based system 3 1 Introduction In this chapter we discuss the structure of a micro controller unit MCU based system that will be used to build our applications We will first talk about why we choose the 8051 as our processor and we will introduce the 8051 family members and their differences Then we will discuss the fundamentals of the 8051 processor In particular we will discuss the memory model the internal registers and their usage Then we will discuss in detail the design of the 8051 single board computer SBC which is the heart of our robot system Finally we will talk about the peripheral chips of our system and their functions 3 2 Micro controllers Why What How So why do we use a micro controller for the soul of our robot and other applications It is simply because micro controllers are cost effective and small enough to fit into our design In fact micro controllers are so common that it can be found in washing machines microwaves
12. an be upgraded later to use other faster and powerful processors of the family with minimum modification of the software drivers So what exactly is a micro controller In fact it is a full functional computer on its own hence it is also called a single chip computer meaning it can compute and think by itself A typical micro controller e g 8051 may have the following modules Exercise3 1 Discuss the differences between the two terms micro controller and microprocessor CPU Central Processing Unit Some internal data Ram e g 128 byte and a few e g 4 8 kilobytes of program ROM Hardware interrupt mechanisms e g 5 different interrupt sources Parallel e g 24 bits input output bus so that it can communicate with the outside world A serial input output so that it can make more distant communications with other computers Timers for counting or generating exact timing output signals for control purposes Power down circuit to keep the internal data even the main power is cut off When it happens the internal data ram can be supported by a small rechargeable battery When the main power comes back the rechargeable battery is recharged again for the next power failure This feature is essential used to maintain continuous service when the power may be cut off occasionally eoo uhan LJ x 3 T RXO P3 31 P Ei Ys TxD P3 3 E ave PROG INTO P3 FJ PEEN NTI 7 ats TO 5 A14 CTi
13. ch determines the operating frequency of the system and a reset switch that starts the program from a reset location Our system uses a clock of 11 0592 MHz it is the basic clock for generating memory read write cycles baud rate for the serial port and the main clock of the internal timers After the reset switch is depressed the microprocessor first loads the content of a startup location from the startup ROM e g 0000Hex for 8051 Then it executes the content of the startup program usually it is a long jump to the ROM space for the starting point of the booting program says the boot loader Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a 3 5 The 8051 system architecture To understand the operation of the 8051 based system we need to study how data and programs are stored in the system Here we will examine two memory storage subsystems gt The 8051 memory model gt The 8051 internal registers 3 5 1 The 8051 memory model This is the memory model of an 8051 micro controller Figure 3 3 memory model of an 8051 micro controller external memory 8031 memory nodel addresses EN noyx Drogam cownter points D use mav Botetan to the addressand exernies the code mmie dict acdress mov adduecadets indirect addversing gt mov Ri data The 8051 memory model has 3 parts A the internal RAM inside the MCU B the external data space c the external program space as depi
14. cted below Internal address RAM in Hex External address space in Hex inside the MCU outside the MCU 00 gt FF 128 bytes Data 64K bytes Program 64K bytes o 80 gt FF special function 0000 FFFF 0000 gt FFFF registers 00 gt 7F 4 register banks RO R1 R2 R3 The lower addresses of the internal RAM contain 4 data register banks RO R1 R2 R3 for the program to store temporary data Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a The upper internal RAM contains the Special Function Registers SFR for storing various operating data e g program counter stack address registers etc for the MCU They can be accessed by the direct addressing method mov instructions The external data memory can be accessed by the movx instructions The external program memory is used to store programs Table 3 1 internal RAM usage and Special Function Register SFR map 1 RESPESEERRRERERaD SRSRSSSRDSSSRRIa SFA Map Indicates Resident in 80525 notin 051a Address location H hex Content 80 FFH Special function registers SFR 30 7FH 64 bytes Scratch pad area for stack 20 2FH 128 bits Bit addressable segment 18 1FH 8 bytes RO R7 bank3 10 17H 8 bytes RO R7 bank2 08 OFH 8 bytes RO R7 bank1 00 07H 8 bytes RO R7 bankO You will find this table useful when we talk about the programming of the 8051 in later chapters
15. ee that the 8031 micro controller uses a technique called time multiplexing it multiplexes data and address bus together For a 64K byte ROM it needs 16 bits address and 8 bit of data so a total number of 16 8 24 bits are required However by multiplexing the two sets of signals together we can save 8 bit of signals so as to reduce the size of the bus To achieve this goal an additional device an external device 8 bit latch is needed to hold the address bits when they appear when ALE is high and use it later on we see how it woks in the following diagrams 270251 4 EXTERNAL PROGRAM MEMORY READ CYCLE Figure 3 5 External program memory read interface block diagram and timing diagram 3 8 2 External Program MEMORY ROM interface The timing diagram is shown above When the 8031 wants to read program code from external memory it acts as follows d It first sets up ALE address latch enable and PSEN program access enable to high The 8031 outputs address bits AO A7 at port0 P0 0 P0 7 and outputs A8 A15 at port2 P2 0 P2 7 Then the 8031 resets ALE to 0 to signal to the outside circuit that address bits at port0 are needed to be latched An 8 bit latch usually a 74373 with latch input LE connected to ALE will do it fine and the address bits a0 A7 are latched at the outputs of the latch 74373 Also PSEN program store enable is reset to 0 as an effect the ROM responses to give the data stored at t
16. he address pointed by AO A7 amp A8 A16 to the data bus connected at PO The 8031 at this stage will read latch the data inside at the rising edge of PSEN through the port PO Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a 3 8 3 External Data Memory RAM interface The standard memory read procedure would now be explained The configuration is very similar to program read instead of using PSEN for accessing the ROM it uses RD and WR to access the RAM As you may aware that RAM is read and write allowed therefore two pins are designated for data memory interface Here are the block diagram and the timing diagram As you can see address data time multiplexing is also used here 270251 5 Figure 5 Accessing External Data Memory If the Program Memory is Internal the Other Bits of P2 are Available as 1 0 EXTERNAL DATA MEMORY READ CYCLE ALE PSEN RD PORTO 42 15 ROW ID PORT2 ALE a _ SLY woe 5 P2 7 OF AN ATS raw OF Figure 3 6 External data memory read interface block diagram and timing diagram Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a 10 3 9 The 8031RL Single Board Computer SBD Design We now uses a SBC called 8031RL which is versatile and cost effective design to illustrate the design of a typical system See http www cse cuhk edu hk khwong ceg3430 803 Irl_schematic_vert jpg gt
17. mable array logic circuit GAL 18CV8 for address decode So that if necessary one can change the address map by changing the content of the GAL chip The connections are as follows Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a PSEN Program enable select of 8031 is connected directly to the OE of the EPROM Therefore only external program can be read from this EPROM Since it is an 8031 same as 8051 with pin EA 0 chip so no programs would be found within the MCU all programs should be stored externally The address decoder output for the range 0000 7FFFH is connected to the CE of the EPROM We see that upper address lines A14 A15 are used for address decode to point to the EPROM chip And lower address lines AO A13 are used to address to memory addresses within the memory chip Figure 3 7 An 8031 and UV EPROM 27256 interface 0000 7FFFH program read select output 32K byte EPROM 27256 Address A15 PSEN decoder RNR 18CV8 ALE P00 P07 A0A7 D0 D7 Address dat _ multiplexed P20 P26 A8 A 14 PSEN 3 9 3 8051 and external data RAM interface Our system uses an SRAM 62256 U6 in the 8031RL schematic as the data memory store The circuit is a similar to the MCU EPROM circuit which also requires the 74373 to latch the address The ALE of 8031 is connected to latch input LE of 74373 And the system uses a programmable array logic circuit GAL 1
18. motor cars or even inside you Octopus smart card So the next question is what type of micro controller should we use We chose the 8051 because of its popularity and cost effectiveness Moreover there are plenty of public domain software as well as commercial libraries available in the industry The 8051 or the ROM less version 8031 is originally an Intel product 1 a cousin of the 80X86 family designed for the embedded control market in the 80s As popular standards especially software standards don t easily die down it flourishes for years and becomes one of the most popular 8 bit micro controllers worldwide It was in the 90s that some other companies jumped into the bandwagon and built faster and more complex micro controllers based on the 8051 core That means the whole library of 8051 assembly code can be reused The representatives of such products are flash based Amtel 8951 7 and the Philips XA 16 bit extended architecture micro controllers 5 They can run as fast as 30MHz and the Philips XA even has a small network standard Controller Area Network CAN 5 of its own for inter micro controller Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a communications a microwave oven can talk to a refrigerator etc The limitation is therefore left for designers imaginations In our discussion will still use the humble 8051 the core design common to all members Nevertheless the system developed c
19. nal RAM2 and IO addresses F000 F002 LCD con2 EC00 ECOD CS of DS1287 real time clock E800 E803 8255 U8 E000 E003 8255 U9 8000 DFFF External RAM2 62256 U7 Internal RAM External External data of 8031 RAM1 Program ROMI1 Special function 0000 registers SFR 80 0000 FF 7FFFH 7FFFH Stack IC 62256 C 27256 30 7F U6 U5 Bit addressable segment 20 2F 128 bytes RAM 00 1F 4 registers banks RBO 1 2 3 End of this chapter 18 Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a 19
20. nt cycle 15 Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a e The monitor program at the 8031 can provide the necessary library i e serial interface drivers for the target program to call from It is in fact akin to system calls of an operating system e It supports any programming languages as long as the output of the cross compiler at the PC is the object code understood by the 8031 We will discuss it more in the chapter on software development In order to save space and complexity the whole address decoding job is handled by the programmable logic device PEEL GAL 18CV8 as follows A10 A15 range of 8000 DFFFH gt CS PSEN PSEN or RD OE of RAM2 U7 RD WR PEEL GAL Program data of 8031 18CV8 used as address decoder CS of RAM1 U6 ICS of ROM1 U5 ICS of 8255 U9 ICS of 8255 U8 Figure 3 12 Address decoder circuit and truth table diagrams are from the 8031RL SBC manual from Cache computer Exercise3 15 Write the Logic formulas of the decoding circuit in term of A0 i A15 RD WR PSEN whichever applicable Use loosely decoding method i to reduce the complexity i e you don t need to decode the exact locations The result would be acceptable as long as the addresses do not overlap External address range Device and pin Formulas name Program 0000 7FFFH CS of ROM1 Data 0000 7FFFH CS of RAMI Data 8000 Data DF FFH
21. om cache computer see http www cse cuhk edu hk khwong ceg3430 803 Irl_schematic_vert jpg In the above discussion we have a system that has 64 Kbytes ROM space for program and also 64K bytes for data storage We should be happy about it However this set up is not suitable for program development why Since you need to develop the program in the hard way such as gt Usea PC to write your program gt Make UV EPROM or ROM that has the object file or machine code or the program gt Insert the ROM into the circuit board The main problem is programming the UV EPROM once will take 10 minutes and it is too long for a debug cycle So the ideal way is to have an operating System O S sitting on the SBC and a user is able to write program run it and debug it interactively with the operating system But our SBC system is too small to have everything inside so some people developed a scheme for developing a small SBC system with the assistance of a Personal Computer It is a method using a monitoring ROM similar to the BIOS of your PC in fact it is a small operating system in the SBC which looks like the following Write your program using the editor on a host PC Compile your program in the PC and generate an object file machine code for 8051 Download the object file to the program RAM of the 8051 SBC RUN the object file at the program RAM ee Mor Mobile Robot chapter 3 The 8051 micro processor based computer system
22. ted as data store when the 8031 executes external data read write instructions to access data in this address range 13 Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a 14 It is treated as program store when the 8031 is reading program instructions within this address range So how to design a circuit to have such functions It is done by a careful design of the chip select decoder for the CS and OE pins of RAM and ROM devices using the following rules ROMI Program retrieval PSEN 0 address range is total 16 bit 64K bytes RAM1 for data only range 0000 7FFFH a Data memory read RD 0 WR 1 PSEN 1 a Data memory write RD 1 WR 0 PSEN 1 RAM for data and program range 8000 FFFFH Data memory read RD 0 WR 1 PSEN 1 Data memory write RD 1 WR 0 PSEN 1 Program memory read PSEN 0 Program memory write never happen Exercise3 12 When will an 8051 read in instructions from where and how Exercise3 13 What 8051 signals are involved during 1 data write 2 data read Mobile Robot chapter 3 The 8051 micro processor based computer system v 4 a 3 9 5 Address decoding So this is the decoding table used in the 8031RL SBC computer is logical AND is logical OR ROM 1 0000 7FFFH 32K program CE A15 for all addresses 0000 7FFFH has A15 0 OE PSEN RAM 1 0000 7FFFH data only E CE amp A15 for all addresses 0
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