Serial 7-Segment Display
Contents
1. 0x31 0x32 0x41 0x42 Any combination of the two will work as well r sparkfun com pe 6175 LONGBOW DRIVE SUITE 200 zP cone 80301 ZIP CODE zP cove 80301 303 NICS BOULDER COLORADO USA Serial 7 Segment Display 2010 05 17 To display a blank digit send the special character x 0x78 Example To Display 42 Blank followed by 42 followed by blank send 0x78 0x04 0x02 0x78 NOTE You must always send your data in 4 byte packets Displayed Character on mo 001 Li Table 1 2010 SparkFun Electronics Inc All Rights Reserved Product features specifications system requirements and availability are subject to change without notice Serial 1 7 Segment Display COM 09230 is a trademark of SparkFun Electronics Inc All other trademarks contained herein are the property of their respective owners FA Serial7SegmentDisplay_DS 092705 X ROHS spar fu LECT NICS Special Commands There are eight special commands that can be sent to the Serial 7 Segment Display Each special command consists of sending a command character followed by a data byte After sending a special command the characters previously on the display will be restored Decimal Point Command To turn on or off any of the decimal points colons or apostrophes on the Serial 7 Segment Display first send the special command character 0x77 followed by a data byte Each of the six least significant bits in the data byte represe2. Digit 4 Control 0x7D Ox7E 6175 LONGBOW DRIVE SUITE 200 BOULDER COLORADO SA 2 COE 80301 303 zee g l Serial 7 Segment Display 2010 05 17 4 Hardware Specifications There are two methods of sending serial data to the Serial 7 Segment Display TTL level serial communication or SPI 4 1 TTL Level Serial Communication When using this method of communication only one wire is needed to interface with the display RX RX is a serial input of the display By default communications will occur at 9600bps with 8 data bits no parity and 1 stop bit The baud rate is adjustable as discussed above in section 3 3 4 2 SPI Communications When using SPI to communicate with the display three wires are used MOSI CSN SCK CSN selects the display in a multiple slave SPI bus SCK is the serial data clock and MOSI is the data line between the master and slave MOSI CSN and SCK are all inputs The Serial 7 Segment Display is configured to be the SPI slave The maximum speed of the SPI clock input is 250kHz The display is configured to use SPI mode 0 CPOL 0 CPHA 0 so the clock line should idle low and data is sampled on the rising edge 5 Electrical Characteristics The backbone of the Serial 7 Segment Display is Atmel s ATMega168 and as such most of the electrical specifications are derived from that The display can be powered at anywhere between 2 6 to 5 5V however there is
3. no on board voltage regulator so anything outside that range could damage the display A logical high voltage on all serial lines should not exceed VCC 0 5 V 2010 SparkFun Electronics Inc All Rights Reserved Product features specifications system requirements and availability are subject to change without notice Serial 3 7 Segment Display COM 09230 is a trademark of SparkFun Electronics Inc All other trademarks contained herein are the property of their respective owners FA Serial7SegmentDisplay_DS 092705 X ROHS
4. e rug ae should be 0 the byte would look like 00110000 So send 0x77 0x30 After the baud rate is adjusted the value is written into the processors non volatile memory so it will retain To turn the colon and apostrophe off send the special the same rate upon power cycling character 0x77 and set all bits in the data byte to 0 So send 0x77 0x00 Example to change the baud rate to 4800 first enter i the special command character 0x79 followed by the Brightness Command binary number 1 So send 0x7F 0x01 To control the brightness of the Serial 7 Segment 3 4 Reset Display Display first send the special command character 0Ox7A followed by a data byte The data byte can be a number between 0 and 254 the lower the number the brighter the display Sending the reset display command 0x76 will clear the display and set the cursor to the first digit This command is useful if the position of the cursor is unknown There is no data byte for this command After the screen receives the brightness command the and it can be sent at any time regardless of cursor 2 2010 SparkFun Electronics Inc All Rights Reserved Product features specifications system requirements and availability are subject to change without notice Serial 7 Segment Display COM 09230 is a trademark of SparkFun Electronics Inc All other trademarks contained herein are the property of their respective owners vA Serial7SegmentDispla
5. nt one decimal point or two in the case of the colon a 1 will turn the decimal point BOULDER COLORADO Serial 7 Segment Display 2010 05 17 brightness value is written into the processor s non volatile memory so it will retain the same brightness level upon power cycling Example to set the display to its dimmest level send the special character 0x7A followed by 254 So send Ox7A OxFE Baud rate control By default the UART baud rate of the Serial 7 Segment Display will be 9600 This can be adjusted by first sending the special command character Ox7F followed by a binary number between 0 and 6 The table below shows corresponding baud rates to data bytes on a O will turn it off The most significant bits in the data byte has no effect on the display The two colon LEDs are connected internally and cannot be Baud Rate Data Byte Value controlled individually The following figure shows the bit representation for each decimal point 0 is the least 2400 0 significant bit 4800 l DIGIT 1 DIGIT e DIGIT 3 DIGIT 4 9600 2 A heh Neh i i i 5 l 5 l l 14400 3 4 Ke SS Ho H Hei H H H 19200 4 yro ro wro yro 0 Z 3 38400 5 Example To turn solely the colon and apostrophe on 57600 6 first send the special character 0x77 The 4th and 5th bits in the data byte should be 1 everything else a ne py no ence a n
6. spar LECT Overview The Serial 7 Segment Display turns the thirteen pins necessary to control a 4 digit 7 segment display into just one or three The display will give you full control of all digits decimal points the colon and the apostrophe At the heart of the display is an ATMega328 which both listens to the serial commands and controls the 7 segment display Features e 4 digit alpha numeric display with serial or SPI interface e Display numbers most letters and a few special characters e Individual control of decimal points apostrophe and colon e Selectable brightness e Baud rate and brightness values retained in non volatile memory e Individual segment control for each digit Interface Specifications The Serial 7 Segment Display can be controlled in one of two ways 1 serial TTL communication or 2 SPI serial communication Regardless of which method you use to communicate with the display you must always send your display data in 4 byte packets and special commands in 2 byte packets Displaying Numbers The first byte you send will correspond to the left most digit on the display the second byte corresponds to the second digit and so on The display can represent all numbers 0 9 and letters A F To display a number you can send either the binary or ASCII representation Example To Display 12AB The user can send numbers in binary representation 0x01 0x02 0x0A Ox0B ASCII representation
7. y_DS_ 092705 X ROHS s position 3 5 Single Character Control Single character control allows you to control each LED of each digit individually Four special commands are used for single character control one for each digit 0x7B controls digit 1 Ox7C controls digit 2 Ox7D controls digit 3 and Ox7E controls digit 4 The special command will be followed by one data byte Similar to decimal point control each bit in the data byte represents a single LED a 1 will turn the digit on a O will turn it off The most significant bit of the data byte has no effect on the display The following figure shows the bit representation for each decimal point 0 is the least significant bit Example To illuminate the B E and G segments of the third digit first send the digit 3 single character control command 0x7D followed by a data byte with the 1st 4th and 6th bits set 0x52 So send Ox7D 0x52 Table 3 Special Command Summa Special Command Byte ASCII Character Pata Byte Value Decimal Each bit controls Point 0x77 w individual Decimal Control 0 254 higher ngniness Ox7A z numbers mean Control Baud Rate Control ORT DEE Reset P Displa ORPOA Digit 1 Control Each bit controls individual segments 0x7B Each bit controls individual segments Digit 2 dia Control 0x7C Each bit controls individual segments Digit 3 Control Each bit controls individual segments
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