1024MAK wrote:A secondary diagnostic microcontroller.
This is a cleaned up "Issue 7.5" based off the US.5 PCB mods to the Issue 6/7 schematic. It fixes the worst sins of the 80s designs by incorporating the small and simple changes everyone always wanted.
Changed:
4 layer board with full ground layer for clean signals/power.
The old board suffered from ground bounce, plus poor power design, mostly originating from the 16 RAM ICs.
8301/8049 moved to the CPU side of the data bus.
Reduces opportunity for CPU to be halted during 8301 video generation.
Switch mode power supply.
The 78XX are gone. A standard 2A+ 9v DC adaptor with 2.1mm barrel connector feeds into a very quiet and cool buck regulator circuit.
16x 64Kx1 DRAMs replaced by faster 4x 64Kx4 DRAMs.
The 16 1-bit DRAMs drew a lot of power and were a large switching load on the power supply. They have been replaced by 4x 4-bit DRAMs of a lower power design. The 8301 runs a lot cooler, and system current draw is cut by almost half.
MC1488/MC1489 replaced by ADM208EAR 5V part with onboard charge pump.
Part of this is that the MC1488/89 required +/-12v, and using a more modern part simplified power supply requirements.
All ICs are DIP and socketed in good quality sockets.
Highly serviceable. Designed to be easy to maintain or repair for the long haul.
All passives are now SMD.
This cleans up the board, reduces component and assembly costs, and frees a lot of board area for.... future projects.
Cleaned up microdrive circuitry on main PCB.
It had a hard time, with the power supply and video circuitry right next to it. With that gone, it has room to be more modular and organized in layout - not just crammed into the remaining space.
Changed how microdrive PCB fits on motherboard.
Microdrives now plug directly onto PCB, no cable. They have a pin array on the back which pushes down onto a socket on the PCB. It makes removing and reinstalling them MUCH easier, and the connections are much more secure.
Two replacement microdrive PCBs are part of the layout.
Redesigned 4 layer PCB, other changes include giving clean 5v instead of 9v so no regulator on board - keeping your fragile microdrives away from heat sources.
DB9 serial/joystick.
Can't get the old sockets. Wouldn't use them if I could. Joystick would be Kempston compatible layout, unless feedback tells me to do different. Serial, I can either follow the German QL pinout or standard 9-pin PC serial layout.
ROMOE jumper.
Select if using Sinclair ROMs or an EPROM - inverts the chip select signal.
Reset button.
I couldn't find a good source for the QL reset button, so I have replaced it with an upright tactile switch.
Serial headers.
You can disconnect internal serial from the DB9s and hook up the SuperHermes serial. Maintains the clean lines of your QL without bits hanging out of it.
Fits in existing case.
All socket positions, mounting holes, etc. are in the same place. Put it in your QL case and nobody will know. Unless you're english, in which case you will need to remove some plastic at the back of the case for the DB9 sockets - then it will look exactly like a German or US QL.
Added:
New GAL replaces IC38 HAL
Revised logic, primarily focused on improved handling of /DTACK. Replaces 8301 decode functionality. Also, a bit of future proofing.
Deleted:
MC1377, UHF modulator and related circuitry.
Who uses UHF any more? It is quite hard to find all the parts now. I decided to leave some space free to have the option of adding a SCART connector and/or S-Video/composite. All video signals are buffered and shock protected, so no more blown up 8301s.
Not changed:
Expansion port, ROM port, RGB functionality, microdrive capability, QLNET, sound (now buffered), keyboard, board shape/size, microdrive expansion port, component positions. All previous internal expansions will fit, including (Super)Hermes. Included headers so you can disconnect internal serial from the DB9s and hook up the SuperHermes serial.
I can see anyone using an issue 5 board buying this as an upgrade, and anyone with a bad issue 6 or 7 board might buy this as a service/replacement part. It's ideally suited to large systems that are heavily expanded with (S)GC, etc. etc.. Just provide a 3A 9V supply.
I do have options for future revisions. However, this board isn't about big changes. It's about refining the current design in a 100% compatible way. I have been incredibly slow about releasing anything. I think this board being in people's hands will maybe change some minds and I might get a couple more offers of help with other projects that need coding support. (See separate post)
So, bear in mind the character of the board - it is very definitely an Issue 7-like board, with just modernised component selections and fabrication technologies. Think of it as just a new 100% QL board.
With that in mind, the engineers, developers, etc... What signals would you like brought out to test points?