Hi,
I know more about OPDs than QLs.
One of the later additions to the OPD was a RAMCAP. This was a bank of volatile RAM , I think 512k , backed up with a battery that plugged into a capsule socket on the OPD. This is where OPD software was held in ROM. It enabled the OPD to write to it and it was saved even when the machine was turned off. I'm pretty sure these were only used for software development for OPD applications in ROM.
Was anything like this developed for the QL.
I'm guessing that the architecture for something like this must be very similar between the OPD and QL.
Thanks
DAve
Battery backed ROM
-
mk79
- QL Wafer Drive
- Posts: 1349
- Joined: Sun Feb 02, 2014 10:54 am
- Location: Esslingen/Germany
- Contact:
Re: Battery backed ROM
I had something similar to this (see left side of my QL picture here https://www.kilgus.net/ql/my-ql-of-yore/). But that was a private development of a friend of mine and probably only a dozen cards or so were ever built.
Re: Battery backed ROM
It could be done on the QL but probably not with 512k unless there was less real RAM, because the memory has to be mapped somewhere.
The Maxim/Dallas chip is the key on that board, it is there for proper detection of power supply fail, so the chip prevents accidental writes to the RAM and switches over to battery bakup and back when appropriate. I am guessing the switch is there to write protect the RAM.
These days there would be a simpler way to do it, using a zero power SRAM package, which has all of that already integrated into the chip, including battery. These are commonly used to emulate ROM, but they do need a small PCB with some minimum hardware to implement write protect and re-route some pins as the SRAM chip has a slightly different pinout in some cases.
The board on the picture also has a MCM (multichip module) wit probably 4x 128k SRAM, two on each side - beck then 512k SRAM in one chip was not available, today it is easy to find, so the whole circuit would be additionally simplified.
The Maxim/Dallas chip is the key on that board, it is there for proper detection of power supply fail, so the chip prevents accidental writes to the RAM and switches over to battery bakup and back when appropriate. I am guessing the switch is there to write protect the RAM.
These days there would be a simpler way to do it, using a zero power SRAM package, which has all of that already integrated into the chip, including battery. These are commonly used to emulate ROM, but they do need a small PCB with some minimum hardware to implement write protect and re-route some pins as the SRAM chip has a slightly different pinout in some cases.
The board on the picture also has a MCM (multichip module) wit probably 4x 128k SRAM, two on each side - beck then 512k SRAM in one chip was not available, today it is easy to find, so the whole circuit would be additionally simplified.