Using a 16K Memotech Memopak That Has Switches

This was in a letter that I wrote to Gilliam Parrish in regards to using a 16K MEMOTECH MEMOPAK.

At the Dayton ComputerFest I did find a 16K Memotech ram module of the latter manufacture with the DIP switches which are located where the oval opening in the back is. I really did not know that they made two versions but am not surprised. And I would expect that it could be possible to upgrade a switchless version to one with switches. How much circuitry would have to be changed is not known. But the switchless version will not work with more than 16K of memory.

But this is what the manual stated:

HOW DO I SET UP THE MEMOTECH 16K?

Make sure your power supply is not connected to the ZX81 when you attach the pack. We recommend that the ZX81 + (this was wrote in the U. K. where they never had the T/S 1000) MEMOPAK configuration should go in this order, according to what add-ons you have:

ZX81 + (Commercial Printer I/F) + (HRG) + Master Memopak 16K or 32K + (Sinclair Printer – Silver paper one) + (Slave Memopak or Sinclair 16K). (You will have to experiment to find out where to connect the T/S 2040 printer.)

WHAT ABOUT THE SWITCH SETTINGS?

There are two possible modes for using the Memopak 16K: MASTER and SLAVE. The mode you require depends on which of the possible memory configurations you are using. The configurations and modes are as follows:

a) MEMOPAK 16K alone (MASTER).
b) MEMOPAK 16K (MASTER) + MEMOPAK 16K (SLAVE).
c) MEMOPAK 16K (MASTER) + SINCLAIR 16K (SLAVE).
d) MEMOPAK 32K (MASTER) + MEMOPAK 16K (SLAVE).

Now, if your MEMOPAK 16K is being used as a MASTER (alone or with a SLAVE pack attached somewhere behind) then switches 2 and 3 should be ON and switches 1 and 4 should be OFF. On the other hand , if your MEMOPAK is sitting behind a MEMOPAK 32K or another 16K then it should be switched into SLAVE mode (1 and 4 ON and 2 and 3 OFF).

REMEMBER “ON” IS UP.

WHAT SHOULD I DO TO USE THE NEW, LARGER MEMORY?

If you have a total of 32K RAM then to make the most of it you’ll need to key in:

POKE 16389,192
NEW

To raise the RAMTOP. For the 48K RAM, you should key in:

POKE 16388,255
POKE 16389,255
NEW

To check RAMTOP, type in:

PRINT PEEK 16389
NEW

and you will get back the current RAMTOP. This should be 192 for 32K of memory. If I remember right 2K should get 72, 16K should get 128, 32K should get 192. Remember that the default is to 16K (128).

With 32K of memory you will have to watch that the display file does not straddle the 32K mark (ROM is 8K, 8K is set aside for use of some accessories) which is where the RAM starts at 16384 (16K times 1024). And that means that 16K of RAM has a RAM top of 32768. So you need to fool the computer and jump the program above the 32768 mark and later that can be edited out of the program.

If you wanted to convert your old style 16K MEMOPAK to the new style Dan Elliott probably could do it. But on the other hand it might be cheaper to go to a new MEMOPAK or a static RAM memory. 0/0