The Sinclair QL Forum

getting some flux on the suspected joint, and then 'sweating' the joing using hot air gun or soldering iron applied somewhere the heat can transfer can sometimes fix these hidden joints.

They can be a pig to find though...

I've used that trick before too

Luckily - although with an exception or two - the manufacturers of these memory chips did agree something of a standard.

If you put the 32 pin chip in the 28pin socket, so that chip is aligned such that the pins furthest away from the notch or spot on the chip are flush with the socket pin ...

It's not a bad idea to wire a resistor - say 470 ohms between the switch common and ground too. That way the signal going to the eprom is either ground or 5v, but never floating.

I can't see any reason why that would not work in theory - with a switch to select the top address bit in the eprom / flash rom to switch between the 2 versions

Hi Will,

I suspect from when IPL is asserted on your pistorm to when you process the read to the IPC is probably a lot shorter than the sequence on a real QL - so it may then be some sort of timing issue. Generally I think the IPC is just polled by the ZX8302 as part of the 50Hz (regular frame ...

Looking at your state machine logic - you sample VPA in state 4 - but it seems to be implied that this is for VMA access (6800 series Synchronous access).

The VPA signal has 2 purposes on the 68000/68008 - it is either used for the above purpose - or to respond to an interrupt acknowledge cycle ...

This is the routine for sending bits in the original IPC:

; send 4bit data to ZX8302, ent A.msb=data
0762: BF 04 MOV R7,#04 Load loop counter for 4 bits to send
0764: AE MOV R6,A
0765: 0A IN A,P2
0766: 53 80 ANL A,#80 loop until comdata=H These 2 lines loop around until the comdata line goes high ...

sounds like a good idea for a project!

I am working on getting something along the lines of a SuperHermes lite (hermes with PS/2) with some some SuperHermes functions included (mainly using the onboard NVRAM on the PIC), but getting the whole thing to fit into the 40 pin IPC socket. I don't need ...

It will depend a bit on which IPC you are using. It would mean counting the states / cycles for the instructions between setting the row address and then reading the column data in.

In the original IPC code:

; scan keyboard, entry A (one bit=1), ret A
05C8: 39 OUTL P1,A output A on P1
05C9: AB MOV ...