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Psion Organiser One

Schematic for the 8KB DataPak.
[8KB DataPak]

Now, then, I've mentioned those Datapaks before. Are you getting curious about how they work?
after all, not many computers use EPROM's as data storage.

Here's a table of the connector pins and their usage:
EPROM programming
Program signal
voltage GND
'Chip Enable'
'Output enable'
Counter Clock/
Counter RESET
Data 6 Data 7
Data 4 Data 5
Data 2 Data 3
Data 0 Data 1

To make it easier discernible, I've coloured Power in RED, signal and address in BLUE and data in GREEN colours. Note, I'm NOT certain about the organisation of the DATA lines. I've numbered them after which pins they connect to on the EPROM, but the Organiser may use them in a different order.

Also, the address lines does NOT match the counter output directly. This only matters if you try to read the EPROM in a EPROM programmer. (Because the data isn't in the conventional order.)

Now, for an explanation...

As you can see, there's no address lines(not counting the Clock/A0 signal) passed on to the connector, so how do we address it?
The secret lies in the 4040 CMOS chip. this is a counter with 12 outputs.
The Organiser first pulses the Reset line to set it to 0, then it pulses the clock pin, and for every new address, reads off the Data. Yes, it's a slow and cumbersome method of accessing random data, but remember, there's only TWO operations done towards it, writing, which is slow anyhow, and searching, which is sequential...

This means that the Datapak is optimised for two things: a minimal interface, and data retrieval.
Assuming that the Organiser keeps count of the used area, so that it doesn't have to read through it to find room for new data, it only have to pulse the counters clock chip enough times, and that can be done with reasonable speed.

I have no idea what the 3pin surface mount chip marked in with question marks is. Possibly some sort of Diode? It's marked with 'A4', if that helps...

All 3 resistors are 47.2K Ohm. The two condensators don't have marks, but I doubt that the size is critical.

There's a 16KB module, too, but I haven't examined that yet. It Is different, though, since it uses two 4024 chips instead of the 4040.

Theoretically, you could build a large Datapak, using maybe a 64KB EPROM and using a slide switch and decoder to 'segment' it into different Datapak's.
Then you could have different 'DataPak's' for different databases. Maybe a project for later...

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