[P] MECB I/O and RTC Card

[epaell]

I currently have a working version of the I/O part of this card. It's based on a similar card for the RC2014. It provides a simple 8 bit set of inputs (nominally connected to a set of 8 DIP switches) and 8 bit set of outputs (nominally connected to 8 LEDs). Optionally, the inputs and outputs can be taken out to a so-called front panel via a ribbon cable - The idea is that it can be used to configure the operation of the system (e.g. whether to start up in the monitor, BASIC or boot off a drive) and to give status of the system via the LEDs.

I've also added an RTC (Real-time clock) to this. Again, this is based on a similar card for the RC2014. As far as I can tell it seems to work and it provides access to 31 bytes of non-volatile memory and a battery-powered real-time clock that maintains the date/time even when the system is powered off. One issue I still have with this is that I can't seem to get it to run with RomWBW (a Z80 software base that provides a lot of really nice software).

The current v0.1 boards are available here:
https://github.com/epaell/MECB/tree/main/MECB_IO

[epaell]

I'm still having some trouble with the RTC board. I have noticed that on the rare occasion it will be picked up by RomWBW on start up. Often, when it doesn't get picked up, hitting the reset button will cause it to pick it up. Even when it isn't picked up my test program (which reads and writes a sequence of values to one of the NVM bytes) seems to work absolutely fine and the RTC seems to keep the time as well (at least overnight while I had the board switched off). So I'm a bit stumped. It's like something in the start up of the device is not quite right or something in RomWBW is not initialising it in a reliable manner (though then I would've expected the same issue with RC2014 boards to be reported). The only thing I can think of is that the Datasheet for the DS1302 device I'm using does specify that tracks should not be routed to certain regions around the device - I wasn't aware of this and noticed that there are tracks in those regions. Perhaps this is causing some additional noise that affects the initial start-up.

[epaell]

The application note was a bit of misdirection (it is mainly to ensure accuracy of the clock and shouldn't affect the actual operation of the device). After a bit of checking of the signalling I realised that I neglected to add the active-low state on one of the signals in the schematic and so it wasn't actually connected on the PCB. Adding a bodge wire to make this connection fixed the issue. I'll update the schematic and PCB now to create a v1.0 board which will hopefully just work "out of the box".

[epaell]

I've received the V1.0 PCBs, built them up and confirmed that they now work fine. All of the updated files and PLD definitions are on my GitHub:

https://github.com/epaell/MECB/tree/main/MECB_IO

NOTE: The one aspect I haven't tested is the external front panel interface (which is connected via the header and 3-pin connector. Also note, if using the front panel then the onboard LEDs and switches should NOT be installed.

[djrm]

Hi Emil, A brief not to say the IDE and IO cards are working, Using them withthe keyboard card allows me to auto boot into CP/M using the TMS/PS/2 combination, sweet.

I tried the xmodem flash firmware update today too all ok.

n.b The only LEDs I had eight of were the white SM ones seen here. I'm waiting for a LS174 to arrive before I can test the clock. I'm waiting for one of those small CF sockets too.

[epaell]

Fantastic - thanks for the update David. LOL, you may need to wear sunglasses (or welding mask) when looking at those LEDs

I've made up a PS/2 keyboard board (compatible with RC2014) and am just waiting for the parts to arrive to test it. I'd also like to try my hand at building a C64 SID interface but it might have to wait until more savings come in (maybe another month or two).