ZX81XRAM - external 32k memory module +HRG
Posted: Mon Apr 29, 2013 10:52 pm
Some people saw it already at Mahlerts and here it is. I developed an external memory kit 32k RAM, HRG compatible which is available now for sale.
These are the features of the RAM:
* add-on module for Sinclair ZX81 via ZX81 bus/slot connector (don't need to open/solder your ZX81)
* 32k RAM from address $4000-$BFFF (ROM shadow disabled in $8000-$BFFF)
* automatic memory detection on startup / after reset (no POKE necessary)
* HRG compatible (RAM is enabled during refresh if addressed)
* up to full 32k BASIC
* machine code can be used in first 16k, combination of 16k machine code + 16k BASIC
* no rom pack wobble
* module only 70x55 mm (2,75x2,15 inches) and fits into original Sinclair/Timex 16k memory case "1016" (*)
(*) for putting it into the original case a small modification is necessary as shown below in another posting
This memory module offers more memory than the 16k memory blocks known from Sinclair. Anyway these modules are often faulty due to it's construction with 2 additional voltages (+12V, -5V) created with a simple inductor circuit. If they are not faulty there is a big chance of crashing programs on the ZX81 from time to time, also known as ram pack wobble.
The contents of this old 16k memory blocks can be simply replaced with this module by removing the old board and inserting this module. There is only a small jut which need to be removed with a mini drill set and a cutting disc (see next page). This module can be used for full 32k BASIC programs as well as for up to 16k machine code plus 16k BASIC. The machine code has to be placed into the lower part of memory ($4000-$7FFF) in some REM lines because it can not be executed after boundary of $8000 as this is used for generating video display. The upper part from $8000-$BFFF can be fully used for BASIC or for storing data.
Here are pictures of that module:
This module can be used for ZX80 as well (but only 16k RAM available).
These are the features of the RAM:
* add-on module for Sinclair ZX81 via ZX81 bus/slot connector (don't need to open/solder your ZX81)
* 32k RAM from address $4000-$BFFF (ROM shadow disabled in $8000-$BFFF)
* automatic memory detection on startup / after reset (no POKE necessary)
* HRG compatible (RAM is enabled during refresh if addressed)
* up to full 32k BASIC
* machine code can be used in first 16k, combination of 16k machine code + 16k BASIC
* no rom pack wobble
* module only 70x55 mm (2,75x2,15 inches) and fits into original Sinclair/Timex 16k memory case "1016" (*)
(*) for putting it into the original case a small modification is necessary as shown below in another posting
This memory module offers more memory than the 16k memory blocks known from Sinclair. Anyway these modules are often faulty due to it's construction with 2 additional voltages (+12V, -5V) created with a simple inductor circuit. If they are not faulty there is a big chance of crashing programs on the ZX81 from time to time, also known as ram pack wobble.
The contents of this old 16k memory blocks can be simply replaced with this module by removing the old board and inserting this module. There is only a small jut which need to be removed with a mini drill set and a cutting disc (see next page). This module can be used for full 32k BASIC programs as well as for up to 16k machine code plus 16k BASIC. The machine code has to be placed into the lower part of memory ($4000-$7FFF) in some REM lines because it can not be executed after boundary of $8000 as this is used for generating video display. The upper part from $8000-$BFFF can be fully used for BASIC or for storing data.
Here are pictures of that module:
This module can be used for ZX80 as well (but only 16k RAM available).