How to use TM1637 chip for LED Display?

[Balachandar]

Hi All,

For the past 10 days, I have been trying to make the TM1637 work with PBP 2.60C but till now I have not been successful. It's a real low cost module. The price of the TM1637 4-digit 7-segment 0.36" display module is about $ 0.60 in Ali Express. There is a 0.56" version and that costs about $ 1.25.
The module works fine with Arduino, but all the important instructions to interface with TM1637 are in the library file (TM1637Display.h). After spending some time with the library file, I decided to study the datasheet of the chip and write the required code in PBP. The protocol followed by the chip is very similar to I2C with a few differences. Like I2C, it's a two-wire interface but you can have only one slave on the bus and hence there is no slave address. Secondly, while transmitting a byte, the LS bit is sent first.

The code I wrote for PIC 12F1840 is shown below and it is extremely simple. It should make the number '2' appear on the leftmost digit of the display. When I tested the code, the diagnostic LED blinked, but after that nothing happened. I used Saleae Logic Analyzer to check whether the Clock & Data pulses and Ack were all OK. After some tweaking, I managed to get everything correct (Screenshot file attached). The only issue is, the display shows nothing! Since I know that the module is working fine with Arduino, it's my code in PBP that needs to be looked into.

I would highly appreciate any helpful hint, suggestion or sample code.

- Bala


'---------------------------------------------------------------------------
' This code is for using TM1637 with Four-digit 7-segment LED Display
' with PIC12F1840. Osc is set at 16MHz.
'---------------------------------------------------------------------------
'---------------------------------------------------------------------------
'12F1840 Pinout:
' -------------------------------------------------------
' VDD VSS
' PortA.5 = Not_used PortA.0 = LED
' PortA.4 = Not_used PortA.1 = DIO
' PortA.3 = Not_used PortA.2 = CLK
' -------------------------------------------------------

'@ __CONFIG _CONFIG1, _FOSC_INTOSC & _WDTE_ON & _PWRTE_ON & _MCLRE_OFF & _BOREN_OFF
'@ __CONFIG _CONFIG2, _PLLEN_OFF & _BORV_LO & _LVP_OFF

ASM
ifndef __12F1840
error "12F1840 not selected"
endif
ENDASM

OSCCON = %01111000 '16MHz HF, software PLL disabled
DEFINE OSC 16

'Port direction
TRISA = %001000 'A.3 is input, rest are outputs.

CM1CON0 = 0 'Disable comparator
ANSELA = 0 'Disable A to D

'List of Aliases
LED var PortA.0
DIO var PortA.1
CLK var PortA.2
TrisDIO VAR TrisA.1

'List of variables
Cnt var byte
ByteToSend var byte 'Command or Data byte to be sent

DispCmd var byte
dispcmd = 64 'Command byte for displaying characters starting with the leftmost digit (0b01000000)

Brt8Cmd var byte
brt8cmd = 143 'Command byte for display on with maximum brightness (0b10001111)

Dig1Addr var byte
dig1addr = 192 'Address of digit 1 (left most) (0b11000000)

DispNum var byte
dispnum = 146 ' "2" (Common anode) (10010010)

'Diagnostic routine
DiagRoutine:
for cnt = 1 to 4 'Blink LED 4 times.
led = 1 : pause 100
led = 0 : pause 100
next cnt

goto start

'Subroutines
StartCondition:
clk = 0
dio = 1
clk = 1
pauseus 50
dio = 0 'DIO goes low when CLK is high.
pauseus 50
return

SendTheByte:
clk = 0
for cnt = 7 to 0 step -1 'Send 8 bits of data, starting with the LSB.
dio = bytetosend.0(cnt)
pauseus 50
clk = 1
pauseus 50
clk = 0
Next cnt
'dio = 1
Trisdio = 1 ' Set Data pin direction to input to receive ACK.
pauseus 50
clk = 1
pauseus 50
clk = 0
Trisdio = 0 ' Set Data pin direction back to output.
return

StopCondition:
clk = 0
dio = 0
clk = 1
pauseus 50
dio = 1 'DIO goes high when CLK is high.
pauseus 50
return

START:

bytetosend = brt8cmd 'Brt8Cmd (10001111) (143) = Command for Display On with Maximum Brightness
gosub startcondition
gosub sendthebyte
gosub stopcondition

bytetosend = dispcmd 'DispCmd (01000000) (64) = Command byte with auto increment sent before sending the digit data
gosub startcondition
gosub sendthebyte
gosub stopcondition

bytetosend = dig1addr 'Dig1Addr (11000000) (192) = Address of digit 1 (leftmost digit)
gosub startcondition
gosub sendthebyte

bytetosend = dispnum ' Number "2" (10010010) (146) (Common anode)
gosub sendthebyte

gosub stopcondition


END