mfkiwl / model100-ice40

TRS-80 Model 100 FPGA board

TRS-80 Model iCE100

This replaces the mainboard of the TRS-80 Model 100 with an iCE40 FPGA (or with limited features using a Teensy++) that can act as a serial or graphics console to a USB attached device.

More info: https://trmm.net/TRS80_Model_100

Pinout

The LCD is 240x64 and uses ten Hitachi HD44102 LCD controllers, each with its own select line and shared control lines.

The LCD requires a charge pump to generate the -5V required for the bias voltage. This is generated with a duty cycle controlled PWM output.

LCD connector HU-30P-2G-L13

Pin	Function
1	VDD
2	BZ - buzzer on the front panel (optional)
3	VEE -- negative voltage (-5V)
4	V2 - contrast voltage (0 - 5V)
5	GND
6	GND
7	CS24
8	CS23
9	CS29
10	CS22
11	CS28
12	CS21
13	CS27
14	CS20
15	CS26
16	CS25
17	RESET (can be pulled high for always reset)
18	CS1
19	E
20	R/!W (can be pulled low for always write)
21	D/!I
22	AD0
23	AD1
24	AD2
25	AD3
26	AD4
27	AD5
28	AD6
29	AD7
30	NC

LCD bias voltage

The LCD requires negative voltage, which is generated with a two diode, two capacitor charge pump.

       +
PWM ---||---+--|<--+-- OUT
            |      |
            \/    ---
            --    ---+
            |      |
GND --------+------+

If it is driven with a 3V signal, the minimum output is around -2 V. Driving with a 5V PWM produces -3 V, which gives better contrast.

        5V
         |
         # 100 Ohm
         |
         +-------------- 5V PWM out
         |
         /
PWM ----|
         \
         v
         |
        GND        

Image format

convert -resize !240x64 -depth 1 -monochrome -rotate 90 \
logo.png logo.gray
xxd -g8 -c8 -p logo.gray > fb.hex

Keyboard

The 8x9 keyboard matrix has diodes on every key so it is possible to identify any number of pressed keys. However, due to the direction of the diodes this requires that a slightly odd mechanism be used.

The 8 rows are all configured as input pullups and the 8 of the 9 columns are driven high. All the rows are read and any that have been pulled low due to the diode sinking current to ground are pressed.

      3V
       |
       # internal pullup
       |
Row ---+---->|--/ --- Col

Upduino v2

J6 1.7 5 90 JP6 39.5 1.8 180 JP5 39.5 19.58 180