Anyone who has read the datasheet for the Winstar OLEDs that Rev-Ed sell as part of the AXE133Y should have noticed a brief mention of the SPI interface and a vague description of how the interface works. However it doesn't tell you how to use the SPI interface!
Luckily, badge engineering firm Newhaven Display has found out for us! Some jumpers on the back of the OLED module simply have to be moved around, then the display can be used in SPI mode.
Jumper selections
| MPU interface | L_PS_H | J68_J80 | L_SHL_H | L_CS_H | JCS |
| 6800 parallel (default) | H | J68 | H | L | Don't Care |
| 8080 parallel | H | J80 | H | L | Don't Care |
| SPI | L | Don't Care | H | Open | Short |
Pinout of the OLED module in SPI mode
| Pin | Symbol | Function |
| 1 | Vss | Ground |
| 2 | Vdd | Supply voltage |
| 3-11 | NC | Not connected |
| 12 | SCL | Serial Clock Signal |
| 13 | SDO | Serial Data Output Signal (connected to PICAXE data input where used) |
| 14 | SDI | Serial Data Input Signal (connected to PICAXE data output) |
| 15 | NC | Not connected |
| 16 | CS | Active LOW Chip Select signal |
As you can see here, the RS and R/W bits need to be repeated after each instruction but not after each data byte, which is weird considering it says that CS must go high when switching between instructions and data. In the code example, a single procedure for transmitting instructions will be used and it will make CS low, send one instruction, then make CS high again. It is rare to need to send multiple instructions in a row so there's little point in going to the trouble of enabling multiple instructions to be sent in a single period of CS being low.
The code example is written for the PICAXE-08M microcontroller but can easily be adapted for different PICAXE microcontrollers. Remember that SDO on the PICAXE is connected to SDI on the OLED module. SDO on the OLED module is not used in this example (it's only needed if you want to read from the module).
All SPI transmissions on the PICAXE are bit banged which makes it very slow even compared to the AXE133 serial interface. The situation can be improved by increasing the clock speed but what's really needed is for Rev-Ed to implement this in the PICAXE firmware however this, along with the sale of SPI Winstar OLEDs, is unlikely as it would hurt sales of the AXE133 PCB and only new PICAXE chips would be able to use it effectively anyway.
PICAXE Code Example
Code:
#picaxe 08M
symbol cs = 1 'Connect cs pin of OLED to this PICAXE pin
symbol sdo = 0 'Connect sdi pin of OLED to this PICAXE pin
symbol sdopin = outpin0 'Pin variable must be for the same pin as the sdo pin constant
symbol sck = 2 'Connect scl pin of OLED to this PICAXE pin
symbol lcddata = b0
symbol loopcounter = b1
main:
high cs 'Initialise cs pin to 1
high sck 'Initialise sck pin to 1
low sdo 'Initialise sdo pin to 0
lcddata = %00111011 : gosub instructionOut 'Function Set: 8-bit, 2 lines, font 11
lcddata = %00000001 : gosub instructionOut 'Clear display
lcddata = %00001100 : gosub instructionOut 'Display on/off control: Display on, cursor off, blink off
lcddata = %00000110 : gosub instructionOut 'Entry mode set: Increment, cursor shift
lcddata = 128 'Cursor position: start of 1st line
gosub instructionOut 'Set cursor position
gosub startData
for loopcounter = 0 to 15 'Writes the message to the display
lookup loopcounter,("Winstar OLED SPI"),lcddata
gosub dataOut
next
gosub endData
lcddata = 192 'Cursor position: start of 2nd line
gosub instructionOut 'Set cursor position
gosub startData
for loopcounter = 0 to 15 'Writes the message to the display
lookup loopcounter,(" on PICAXE-08M "),lcddata
gosub dataOut
next
gosub endData
do : loop 'End program
instructionOut:
low cs 'Put cs, sck and
low sck 'sdo in correct
low sdo 'states
pulsout sck,1 'clock in RS (0)
pulsout sck,1 'clock in RW (0)
gosub outByte 'Send contents of lcddata to the display
high cs
return
startData:
low cs 'Put cs, sck and
low sck 'sdo in correct
high sdo 'states
pulsout sck,1 'clock in RS (1)
low sdo
high sck 'clock in RW (0)
return
dataOut:
low sck
gosub outByte 'Send contents of lcddata to the display
return
endData:
high cs 'Set cs high to end data transmission
return
outByte:
sdopin = bit7 'Set sdo to bit7 (of lcddata)
pulsout sck,1 'Pulse clock pin
sdopin = bit6 'Set sdo to bit6
pulsout sck,1 'Pulse clock pin
sdopin = bit5 'Set sdo to bit5
pulsout sck,1 'Pulse clock pin
sdopin = bit4 'Set sdo to bit4
pulsout sck,1 'Pulse clock pin
sdopin = bit3 'Set sdo to bit3
pulsout sck,1 'Pulse clock pin
sdopin = bit2 'Set sdo to bit2
pulsout sck,1 'Pulse clock pin
sdopin = bit1 'Set sdo to bit1
pulsout sck,1 'Pulse clock pin
sdopin = bit0 'Set sdo to bit0
high sck 'Set clock pin high
return