CET360 MICROPROCESSOR ENGINEERING µTerm LCDC
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1. CET360 MICROPROCESSOR ENGINEERING Term LCDC Implementation Guide by J Sumey ver 2 6 20 Mar 2009 Abstract This guide presents the requirements and implementation strategy for adding a multiline LCD display to the CET360 term project Although the contents of this guide should be familiar to all project team members the primary audience is the hardware and software specialists The result of successful application of this guide will be a text only LCD driver module in the form of LCD h interface and LCD c implementation files Table of Contents 1 IM UPOCUAGHOMN ex 22c 82canesshecnacnd cadaanbieeeeanbiaatieaeneieoie einaees alee 2 2 Technical REICTENCES acsvapeces cxecasscesagncsconepedseesapecsnentgossersseacsens 3 3 Hardware Interfacing cceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeees 3 4 Software Programming 42 Aegon eine tain lag tales lee 3 4 1 MCU Interface Select and Operation ccceeeeeeeeeereeee 5 42 LCDC Instruction Set lt incailtihteuethaleieldatelenieliel ts 6 4 3 Memory Mapping and Cursor Addressing eeceeee0 7 AA ECDC Mittal Zatlom scecaccvoteucavaceviortatatncisecsmcake e A EE 7 4 5 Other LCD Driver Routines ccccccceccceeeeeeeeeeeeeeeeeeeees 8 4 6 Scrolling aneri nen GGG Gees 9 4 7 Convenience Macros cccccccccseeseseeeeeeeeeeeeeeeesseeeeeeeeeeeeees 11 5 SA ace he A 8 Ate gh enh neh neh teak teehee ah eek ae 11 6 Referente2. A test run at this point should produce a blank display with a blinking underline cursor in the top left corner Don t forget to adjust the contrast control if need be Once you have that working the remaining routines should be a breeze The following sections provide some hints on what the other LCD driver routines should do 4 5 1 LCD clear position the cursor to 0 0 call LCD_goto 0 0 use a for loop to output LCD_LINES LCD_COLS ASCII blank spaces via LCD_putc reposition the cursor to 0 0 4 5 2 LCD_goto int line int col compute a new display memory cursor address based on the given line amp col use wrCommand with CMD_CSRW to update the LCDC s cursor address CET360 Microprocessor Engineering LCDC Guide v 2 6 Hint be careful of the byte ordering here since the S12 is big endian you ll need to swap bytes before sending to the LCDC 4 5 3 LCD_putc char chr If the given char is not a control character use wrCommand with CMD_MWRITE to output the ASCII character and exit LCD_putc In order to send chr to wrCommand you ll need to pass chr s address using the amp C operator you may also need a typecast here for the control characters listed in figure 9 handle appropriately Ctrl Char Function BS move cursor left one column unless already in col 0 HT move cursor right to next tab stop even multiple of 8 columns LFt move cursor down
3. would be considered private to the LCD implementation and not be made available to the client via the header file In order to design and implement the software driver for the LCD you will need to frequently refer to the LCD controller IC data sheet This reference should be thoroughly reviewed prior to continuing with these notes which are based on this assumption Required technical knowledge of the LCDC is highlighted in the following sections CET360 Microprocessor Engineering LCDC Guide v 2 6 4 1 MCU Interface Select and Operation From section 5 of the RA8835 data sheet Pin Descriptions you will note that the SEL1 pin selects between Intel 8080 and Motorola 6800 modes Although either mode works equally well the 8080 mode with separate RD and WR lines features slightly simpler strobe timing and is therefore recommended For MCU writes the AO address line selects between a data register when low and a command register when high Figure 7 2A in the RA8835 data sheet shows a typical 8080 mode interface and timing details are given in figure 10 3 1 of the data sheet This information is extremely important to both the hardware and software specialists and should be thoroughly reviewed As mentioned previously we will be emulating bus style command and data transfers with the LCDC with our busless S12 MCU module Looking at the data sheet timing diagram of figure 10 3 1 we see the recipe for a MCU write
4. 1 line calling LCD_scrollUp if needed VT move cursor up 1 line calling LCD_scrollDn if needed FF clear screen and home cursor i e call LCD_clear CR move cursor to column 0 of current line Fig 9 Basic Control Character Functions t VT and LF should be able to scroll past the top and bottom lines respectively 4 5 4 LCD_puts char str Call LCD_putc ina loop for each character in the given string just like you did in SCI_puts 4 5 5 LCD_scrollUp forward scroll display screen contents by 1 line Hint advance the LCDC s startaddress SAD1 of your text page by LCD_COLS bytes Dont forget to also clear the newly exposed line at the bottom of the screen See the RA8835 data sheet section 7 13 for additional details 4 5 6 LCD _scrol1lDn backward scroll display screen contents by 1 line Hint see the hint for LCD_scrollUp 4 6 Scrolling What should happen when the LCD screen is filled the cursor is at the bottom right corner and one more character is sent to the LCD module A first possibility would be to start over in the top left corner effectively overwriting the current display This is not considered standard behavior The second and generally accepted possibility is to shift the bottom n 1 lines to the top n 1 lines and continue displaying additional characters on the new bottom line However as you might guess it would be an ugly and time consuming process to move all these charac
5. a block of defines should be placed near the top of your LCD c to define appropriate symbolic names for the various LCDC commands Note that these defines belong in LCD c instead of LCD h because they are used exclusively in the driver implementation and never directly by the client These names also serve to provide a degree of documentation and increase overall code quality Figure 6 should give you the idea LCD Instruction Set from RA8835 data sheet x7 define CMD_SYSTEMSET 0x40 Initialize device and display define CMD_SLEEPIN 0x53 Enter standby mode define CMD_DISPLAYOFF 0x58 Turn display off define CMD_DISPLAYON 0x59 Turn display on etc 13 more lines Fig 6 LCDC Instruction Set Symbolic Definitions As a quick introduction the commands in the system control and display control classes are typically used only once during initialization while those in the drawing control and memory control classes are used for general display content updates CET360 Microprocessor Engineering LCDC Guide v 2 6 4 3 Memory Mapping and Cursor Addressing As documented in the data sheet the LCDC also provides a 16 bit address 8 bit data interface to its own display memory and the TCB1335 board includes 32KB of high speed static RAM at 0x0000 0x7FFF for this display memory The idea here is that your driver has to store ASCII codes in the display memory which results in the respective ch
6. aracter appearing on the LCD screen There are essentially two tricks to making this work correctly 1 The display RAM is on the other side of the LCDC thus the MWRITE LCDC instruction must be used to get the ASCII codes transferred through the LCDC and into the display RAM and 2 The actual screen contents are mapped to a range of addresses in the display RAM thus ASCII codes must be written to specific display RAM locations to have them appear at particular locations on the screen See section 7 10 of the RA8835 data sheet for further details The second requirement is exactly the reason for the CSRW Cursor Write instruction so that you can move the LCDC s cursor around the display RAM thus causing subsequently written characters to appear at controlled locations on the screen The LCDC is also capable of generating pixel based graphics however this feature is not covered in this document For simplification we will initialize the LCDC for no graphics page and a single character display page starting at display memory location zero A 24 line x 53 column text display would therefore require a total of 1 272 bytes of display RAM for a full screen display Note that this small amount of display RAM approx 1 25KB is typical of textual displays However a single 640x240 monochrome graphics page would require 20KB of the display RAM Challenge question how much RAM would be required for a 1024x1024 color graphics dis
7. ch may be null and the array length which may be 0 and takes care of writing out a complete command plus parameters to the LCDC using the lowest level wr LCD routine previously described CET360 Microprocessor Engineering LCDC Guide v 2 6 wrCommand low level routine to write command amp data to LCDC k in command LCD command x parms array of byte parameters length length of parameter array 0 if none g out none Sy void wrCommand Byte command const Byte parms Byte length int i wrLCD 1 command output the LCDC command for i 0 i lt length i output all parameter bytes wrLCD 0 parms i Fig 7 wrCommand Routine Now that we have a series of parameter data arrays and the wrCommand_ routine the LCD_init routine becomes drastically simpler as shown in figure 8 LCD_init KI void LCD_init void initialize LCDC initialize LCD output control lines initialize data direction registers LCDC initializa tion sequence according to data sheet fig wrCommand CMD_SYSTEMSET ParmsSysSet wrCommand CMD_SCROLL ParmsScroll sizeof ParmsSysSet sizeof ParmsScroll 5 more calls to wrCommand here LCD_clear erase all the garbage from power up 8 1 Fig 8 LCD_init Routine 4 5 Other LCD Driver Routines The initialization process is probably the most difficult part of the LCD driver
8. e new cursor location appears in the proper location on the screen The easiest way to solve this problem is have a word variable local to LCD c that keeps track of the current value of SAD1 Thus LCD_scrollUp and LCD_scrol1Dn should respectively add and subtract LCD_COLS to this variable and rewrite this variable to SAD1 via the SCROLL command Then in LCD_goto you would also add this variable to the new cursor address betore sending this value to the CSRW command The second problem is the position of cursor when performing scrolls If the cursor position is not adjusted during the scroll operation it will move away from its current position and possibly even off screen which is quite distracting to the user Indeed the cursor should also move down or up by one line for each LCD_scrollUp or LCD_scrol1Dn call respectively The solution for this would be for both of these routines to first acquire the current cursor position relative to the beginning of the display then to update SAD1 as described in the previous paragraph and then finally to reposition the cursor to the previous relative position To acquire the current relative cursor position these two routines could call a new low level support routine get CrsAddr shown in figure 10 to retrieve the LCDC s cursor address register via the CSRR command and then subtract the current display start address This value would then be used by LCD_scrollUp and LCD_scrol1Dn before ex
9. en in figure 5 would be required CET360 Microprocessor Engineering LCDC Guide v 2 6 Byte rdLCD int reg 1l command rdLCD lowest level routin x in address to read out byte value read to read amp return a data byte from LCDC O data Byte result LCDDDR 0 set I O port to all inputs AO reg drive AO line as given CS LOW assert Chip Select RD LOW assert RD strobe 8080 mode asm nop read setup delay result LCDBUS read datum from LCDC RD HIGH deassert RD strobe CS HIGH deassert Chip Select return result return datum read as result Fig 5 Low level rdLCD Routine 4 2 LCDC Instruction Set Because the LCDC is a fairly complex logic device it implements a number of instructions that may be followed by a variable number of data bytes according to the function of the instruction Section 6 of the RA8835 data sheet Instruction Set includes the instruction set summary table followed by detailed descriptions of each instruction Data sheet section 8 1 2 gives an initialization example which serves as the recipe for setting up the LCDC for which LCD_init has been identified to accomplish You will need to study these sections thoroughly to understand how these instructions are used We will explore LCD_init in more detail in a later section For ease of programming within your LCD module and to eliminate magic numbers
10. ided by the character generator ROM built into the LCDC would fit nicely into a 6x10 character matrix with 1 blank pixel column between characters horizontally and 3 blank pixel lines between character lines Did you notice the top down approach being taken here It all starts with what would the client of your LCD module need to know and do Based upon the above description we have our basic header file designed as shown in figure 3 Obviously this header file would be included by any client wishing to interact with the LCD i e main c LCD h interface for LCD driver define LCD_LINES 24 number of character lines define LCD_COLS 53 number of columns per line void LCD_init void initialize LCD controller void LCD_clear void blank out entire LCD void LCD_goto int line int col move cursor to given line col void LCD_putc char output a single char to LCD void LCD_puts char send char string to LCD void LCD_scrollUp void scroll screen contents up void LCD_scrollDn void scroll screen contents down Fig 3 Basic LCD Driver Header File Moving on to the actual driver itself LCD c this is where we find all the detailed programmatic coding to implement the above functions as well as any additional support routines internal to the LCD driver The support routines would typically be the very low level functions that interact with the LCDC itself Of course these
11. ing From a software implementation point of view the LCDC LCD combination should be viewed as an output peripheral albeit a sophisticated one In a fashion similar to the SCI module CET360 Microprocessor Engineering LCDC Guide v 2 6 previously encountered you should think in terms of a software module consisting of the prescribed c driver file the implementation and a h header file the client interface From a client s i e the main program perspective the following actions would be desirable e initialize the LCDC clear the LCD screen and move the cursor to the upper left corner position the cursor to a particular line and column output a single character at the current cursor position output a character string at the current cursor position scroll the screen contents up one line pan down scroll the screen contents down one line pan up Also the client may want to know the screen geometry in terms of the number of lines and characters per line displayable on the actual LCD The screen geometry can vary from one LCD model to another and may also depend on the character matrix geometry For example the LM2028 QVGA LCD panels display a fixed 320h x 240v pixels Given a 6x10 pixel character matrix layout this panel would then display 24 character lines of 53 characters per line The lines would be numbered 0 23 and the character columns would be numbered 0 52 The 5x7 character bitmaps prov
12. iting by calling LCD_goto getCrsAddr get amp return current cursor address i in none out current cursor address as a 16 bit int Word getCrsAddr Byte parms 2 wrCommand CMD_CSRR NULL 0 issue cursor read command parms 0 rdLCD 1 parms 1 rdLCD 1 return parms 1 256 parms 0 byte swapped Fig 10 Low level getCrsAddr Routine CET360 Microprocessor Engineering LCDC Guide v 2 6 4 7 Convenience Macros One of the neatest tricks of programming in C is the use of the preprocessor s macro feature In the development of embedded system projects the macros shown in figure 11 demonstrate some commonly needed constants and functions The MSB LSB and SWAP macros manipulate a word argument while the PULSE macros may be used to create logic pulses on output pins some handy macros define LOW 0 define HIGH 1 extract most significant byte of a word define MSB w w gt gt 8 extract least significant byte of a word define LSB w w amp Oxff swap high low bytes of a word define SWAP w MSB w LSB w lt lt 8 define PULSE_LO pin pin 0 pin 1 create active low pulse define PULSE_HI pin pin 1 pin 0 create active hi pulse Gl Fl Fig 11 Some Handy Macros 5 Q amp A possible question answer section here what would you like to see here 6 References 1 TCB1335 LCD Module Controller Board User Manua
13. l rev 0 1 Topway Technology Co Jun 2004 2 RA8835 Dot Matrix LCD Controller Specification ver 1 7 RAIO Technology Inc Aug 2006 11
14. operation set the AO line high for command register or low for data register drive CS active low output a byte to the data bus and make sure the I O port is an output pulse the WRite line active low then back to high return the CS back to high oe Given appropriate definitions for LCDBUS LCDDDR AO CS WR HIGH and LOW we can implement a wrLCD routine as given in figure 4 that will output a specified data byte to the appropriate register in the LCDC Observation Did you notice how we jumped from a top down to a bottom up approach here Sometimes in embedded systems development it may make sense to apply step wise development bouncing between top down and bottom up processes to effectively meet in the middle wrLCD lowest level routine to write given data byte to LCDC in reg address to write l command O data x data data byte to write out none Kf void wrLCD int reg Byte data A0 reg drive A0 line as given CS LOW assert Chip Select LCDBUS data send datum to LCDC LCDDDR OxFF make sure I O port is all outputs WR LOW stobe command byte to LCDC WR HIGH CS HIGH deassert Chip Select Fig 4 Low level wrLCD Routine It is also possible to perform read operations from the LCDC This would occur if you wanted to obtain either the LCDC s current cursor position or display memory contents In such cases a low level rdLCD routine as giv
15. play using 24 bits per pixel 4 4 LCDC Initialization In order to initialize the LCDC and therefore the LCD screen display you will need to determine the appropriate data byte values for all the commands from SYSTEM SET through OVLAY and arrange for LCD_init to produce a series of write operations to accomplish the initialization Although you could use the wrLcD low level routine in figure 4 to send out each command and data byte individually 30 writes this would be extremely tedious error prone and difficult to maintain A much better method to accomplish this would be to combine a set of initialization parameter arrays with a new wrCommand routine built on top of wrLCD to off load the grunt work from LCD_init For example the following line of code would encapsulate the 8 data bytes required for the SYSTEM SET command into a data array Note that these values are specifically chosen for the LM2028 LCD geometry a different LCD geometry would require different values const Byte ParmsSysSet 0x10 0x05 0x09 52 55 239 53 0 This definition along with five others for those initialization commands requiring data parameters would be placed at the top of LCD c after all defines but before any routines Once the initialization data arrays are built we next add wrCommand as shown in figure 7 This nifty utility routine accepts three arguments a command a pointer to a parameter data array whi
16. s nition neii e t a bed dari tara hance ba baad de 11 CET360 Microprocessor Engineering LCDC Guide v 2 6 1 Introduction As described previously our microterm project will use an LCD Controller LCDC as shown in figure 1 The particular LCDC IC we are using is the RAIO RA8835 as implemented by Topway on their TCB1335 controller board The RA8835 is the modern version of the 1330 1335 series of LCDC ICs made by Epson Seiko S MOS etc that were popular in the 1990s Form 8 AbyPzZ A ye a s _ _ KS 7s E E EE EE EE E E O a a Fig 1 Topway TCB1335 LCD Controller Board The RA8835 is a programmable controller IC with the following features e can accommodate monochrome LCD panels with resolutions up to 640x256 pixels e supports text graphics and combined modes e built in character generator ROM and support for user defined character generation both RAM and ROM based e programmable cursor control e industry standard 8 bit microprocessor interfaces Intel 8080 and Motorola 6800 modes e 60 pin quad flat package QFP e 2 7V to 5 5V operating supply Features of the Topway TCB1335 controller board include e on board LCDC IC oscillator X1 e on board 32 KB SRAM display memory U1 e 5 0 0 5V operation 13mA typ e on board DC DC converter to generate Vee 20V required for LCD panel e 20 pin MCU interface K2 e 16 pin LCD panel interface K3 We will al
17. so be using the LM2028 LCD panel as the display with the following features e 320hx240v pixels e 3 5 5V operation 3 5mA typ e direct interface to K3 on TCB1335 e LED backlight built in 3 5V 300mA CET360 Microprocessor Engineering LCDC Guide v 2 6 2 Technical References There are two primary references you will need when working with the LCDC one for the TCB1335 controller board for hardware interfacing and one for the RA8835 controller IC for software programming Check the resources page on the course website for links to these two documents You may also need to refer to the datasheet for the particular LCD panel you will be using 3 Hardware Interfacing The TCB1335 is interfaced to a control processor our S12 via 20 pin connector K2 using an 8 bit data bus and a single address line A0 Control lines include an active low chip select CS and either active low read RD and write WR lines in 8080 mode or R W and Enable E lines in 6800 mode The reset RES line needs to connect to the system reset line The choice of interface mode is made via the interface select pin SEL1 also on K2 Because the bus interface mode would not need to be changed once selected this pin should be permanently tied to either Vpp or Vss for a fixed logic high or low respectively Refer to section 4 1 below about how to best handle the SEL1 pin In addition to supplying the board with usual power connections Vpp and Vss you
18. ters and lines programmatically As described in section 7 13 of the RA8835 data sheet Scrolling and shown there in figure 7 24 we can employ the LCDC s inter page scrolling feature to support very high speed CET360 Microprocessor Engineering LCDC Guide v 2 6 hardware assisted display scrolling Although the displayed screen contents will initially be generated from the first page of display memory the 32KB of display RAM on the TCB1335 board can support a large number of display pages The trick to getting display scrolling to work is to manipulate the LCDC s startaddress1 SAD1 register via the SCROLL command For the LCD_scroll1Up function you would add LCD_COLS to SAD1 This effectively moves line 2 to line 1 line 3 to 2 etc and would open a new line at the bottom of the display which you should clear to all blanks This addition process could continue as needed and the 16 bit address counter registers within the LCDC would simply wrap around at the end of the display memory For reverse scrolling LCD_scrol1Dn would subtract LCD_COLS from SAD1 No clearing of the newly recalled line 1 would be needed resulting in the feature to scroll back in display history When scrolling the display contents there are two other small problems that must be properly handled The first problem is when doing cursor addressing in LCD_goto the changing display start address must be added to the new cursor address to insure th
19. will also need an external contrast control potentiometer on your breadboard as shown in figure 2 This potentiometer allows you to adjust the contrast of the LCD panel by varying the bias voltage Vo between Vpp and Vee Finally the TCB1335 also supports backlight power connections for backlit panels by passing through the BLA anode and BLK kathode pins from K2 to K3 LCD panel connection For the LM2028 panel operating on 5VDC a 18 33Q resistor should be used between 5V and BLA BLK must connect to ground Vbo 10 20kQ Vo Vee Fig 2 LCD Contrast Control Recall that the particular S12C32 MCU we are using on the Dragonfly does not implement an external data address bus architecture thus you may think that it is not possible to interface a peripheral type device such as this LCDC IC to an MCU that is missing conventional bus pins Indeed our S12C32 MCU can be described as being peripheral bus challenged But wait this is Microprocessor Engineering all things are possible You will need to work with your team to devise a scheme wherein you can emulate traditional bus operation using the I O pins available on our C32 Hint use port T as a bidirectional data bus and some port M pins for control bus signals as mentioned above plus the AO address line CAUTION Use extreme care when wiring the 20 pin DIP ribbon connector to the TCB1335 this connector does not use standard pin layout numbering 4 Software Programm
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