osresearch/psionpi

Raspberry Pi board to fit in a Psion PDA

Raspberry Pi for the Psion MX series

The Psion 5 MX was a PDA manufactured in 1999 that had a decent physical keyboard in a clamshell with a really unique sliding design that counterbalanced it. You could buy a modern Gemina PDA that has a color screen and a decent processor, or you could try to fit a Pi Zero W and interface FPGA into the twenty year old gadget.

Screen module

The LCD is 640x240 with four levels of gray, a Hitachi SP14H001-T1A, but no datasheet has been found for it. The Hitachi SR16H005 has a similar pinout, and the SR14Q001 has more analog power inputs.

Pinout

Probing the 26-pin 0.5mm FPC connector finds a similar four-bit wide data path, along with pins for the touch screen:

Pin	Function
1	Digitizer X, idle 0.0V, analog pulses
2	Digitizer X, idle 3.3v, roughly every 20 ms
3	Digitizer Y, idle 3.3V, two pulses at a time
4	Digitizer Y, idle 0.0V, differential pairs?
5	GND
6	3.3V (Digitizer power?)
7	LCD Bias voltage +20.0V
8	LCD Bias voltage -15V min contrast, -20V max contrast
9	2.6V Comparator input for Hi-level inputs?
10	1.1V Comparator input for Lo-level inputs?
11	GND
12	Load? 1.4 usec pulse every 59.6 usec
13	CP clock at 2.8 MHz
14	GND
15	Data at 2.8 Mhz
16	Data at 2.8 Mhz
17	Data at 2.8 Mhz
18	Data at 2.8 Mhz
19	GND
20	Frame? 60 usec pulse every 68 Hz
21	3.3V (LCD power?)
22	706 Hz square wave, 50% duty cycle. Not connected on the FPC?
23	GND
24	Backlight voltage
25	GND (But not connected on the FPC)
26	Backlight voltage (~70V?)

The probed pinout matches the block diagram for the Hitachi module. Four data pins, a high speed pixel clock, a latch roughly every 640/4 clocks, and a frame roughly every 240 latches.

Interface

640x240 is 153600 pixels, sent four in parallel, or 38400 clocks per frame. With the measured 2.8 MHz clock, that is 52 frames per second for monochrome. The Psion displays four shades of gray, although it is not clear how this is done; none of the Hitachi data sheets mention it anywhere and high-speed cameras don't seem to pickup any additional flicker from the gray pixels.

Also note that the diagram in the datasheet appears to be double-data-rate on both the rising and falling edge, but this is not observed in practice. The data pins always transition on rising edge and are falling edge clocked.

FPGA interface

• 20 Psion keyboard

• 8 Psion LCD

• 3 Psion digitizer

• 5 Psion switches

• 1 Psion keyboard LED

• ? charge pump PWMs (-17 V LCD bias, +70 V backlight)

• 4 Pi SPI display

• 2 Pi serial console

• ? Pi to FPGA SPI programming

• Battery interface?

• Charger port?

• External connectors?

• CF port?

• IR port?

• Speaker?

• Mic?

up5k has ~30 available IO, so the keyboard takes many of them. Maybe bridge 7-8 so that they use only one input? Would this cause problems with multiple modifiers?

Pi TFT interface

The rpi-display overlay loads the fb_ili9341.ko module, which has a hard-coded 240x320 display resolution. Hacking the binary to change the resolutions at offset 0xC70 to 640x480 works fine. There is quite a bit of artifacting; it might be due to long jumper wires and the 32 MHz clock rate, so this might improve with a PCB design.

Keyboard

RasmusB built a Psion keyboard interface which documents the pinout and 12x8 scan matrix. This has not yet been verified. The ice40up5k doesn't have enough pins to do both the LCD and the keyboard, so a separate MCU should be used like the atmega32u4 with USB. It can also read the analog values from the touch screen sensor and emulate the mouse.

Pinout

The keyboard conncetor is a 22-pin 0.5mm FPC similar to TE Connectivity AMP Connectors 2-1734839-2.

Pin	Function
1	NC
2	Col 9
3	Col 12
4	Col 11
5	Col 10
6	Col 8
7	Col 7
8	Col 3
9	Col 4
10	Col 5
11	Col 6
12	Col 2
13	Row 3
14	Row 4
15	Row 5
16	Col 1
17	Row 2
18	Row 6
19	Row 7
20	Row 8
21	Row 1
22	NC

Scan matrix

	1	2	3	4	5	6	7	8
1		1	7	Q	U	Tab	H	Z
2	Space	2	8	W	I	A	J	X
3	Up	3	9	E	O	S	K	C
4	,	4	0	R	P	D	M	V
5	Left	5	Back	T	L	F	.	B
6	Right	6	`	Y	Enter	G	Down	N
7	LShift
8								RShift
9						Ctrl
10							Fn
11					Menu
12				Esc