Playground I/O PCB with 3x 8bit ports

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  • #888
    Phil_G
    Moderator

    First, apologies for the multiple posts, the forum wont let me post anything with more than one link.

    My 8255 I/O boards arrived via the slow boat from China a couple of days ago, as always JLCPCB do a fantastic job, beautifully made boards at unbelievable prices – less than half of the delivery cost!

    So far I’ve made up four boards but then ran out of 74HC10’s, all test ok at 4 or 10 mhz.
    I’ve fitted one into my RS cased Playground and aesthetically it matches quite nicely 🙂

    I have a few bare PCBs spare if anyone would like one, let me know. You need an SN74HC10, an INS8255, a 14-pin and a 40-pin IC socket, a 36-way socket strip and a decoupling capacitor. Its an easy 2 minute assembly.

    #889
    Phil_G
    Moderator

    On CP/M drive B: you will find MBASIC and heres a simple test program that just waggles all the I/O pins up & down:

    Heres a video:
    https://www.youtube.com/watch?v=cu_yJXgvruo

    10 OUT 35,128:REM SET MODE TO ALL OUTPUTS
    20 FOR A=1 TO 500:NEXT A:REM SMALL DELAY
    30 OUT 32,0:REM ALL OUTPUT PINS TO ZEROS
    40 OUT 33,0
    50 OUT 34,0
    60 FOR A=1 TO 500:NEXT A:REM SMALL DELAY
    70 OUT 32,255:REM ALL OUTPUT PINS TO ONES
    80 OUT 33,255
    90 OUT 34,255
    100 GOTO 20

    #890
    Phil_G
    Moderator

    #891
    Phil_G
    Moderator

    #892
    Phil_G
    Moderator

    As usual, right-click and ‘open in a new tab’ for a full size pic

    And another video, same thing as before but this is the new PCB in the cased Playground:
    https://youtu.be/BWP404CkBA4

    Note that only neg and signal are connected to the Playground – the servo takes a fair bit of current so it gets its pos feed from the NiMh battery pack. Neg is of course common.

    #894
    john
    Keymaster

    I am ecstatic! The first ever third-party peripheral board for the Z80 Playground!!!

    #899
    Phil_G
    Moderator

    I have four of the 8255 boards going spare, free to a good home, any more after these four is no problem but I’ll have to order a batch with costs shared (maybe £3.50 each, UK delivered?). Any takers? philg@talk21.com
    Cheers
    Phil

    Video: https://youtu.be/BWP404CkBA4

    #944
    Phil_G
    Moderator

    A couple of weeks on, and even for free, theres been almost no interest in the I/O board! I cant give them away! and I thought I might need another batch!

    #945
    kevin
    Participant

    I’d be interested, but my Z80-PG is now built into a case. I’ll have to wait until/if I can get another Z80-PG board 😉

    Kevin.

    #950
    johnw
    Participant

    I’m interested! Can you email me at “z80pg at johnwike dot co dot uk” with details.

    #951
    Steve
    Participant

    Hi, for me, I would like to see an expansion board with additional RAM, 512KB minimum, at least one ROM socket, a RTC and maybe 8 I/O pins

    #952
    Phil_G
    Moderator

    That would need major changes to the operating system and the PG though Steve, CP/M 2.2 is unaware of anything beyond the Z80’s 64k memory map so John would probably need to work his magic again on CP/M 3, he’d need to implement paging routines, (probably 32k pages?) and where would the OS put a rom when CP/M relies on the entire memory map full of ram? It would also need address decoding changes to the Playground hardware to enable paging… lots of work for John!
    An RTC can be done via straight parallel I/O (the 8255 could co it), or SPI or I2C (again the 8255 could do either) I used an old parallel MM58174. But generally, more memory isnt a trivial ask 🙂
    Have you made a start on your board Steve, I’d be interested to follow its development… its beyond my own requirements but I’m always interested.
    Cheers
    Phil

    #953
    Steve
    Participant

    Hi Phil

    Yeah I’m aware of the hardware requirements. John’s board would not have to change at all. The additional address decoding etc. would be put on the expansion board. Software wise, the ROM is switched out for John’s CP/M already, so the same would be true for CP/M 3. If the memory map is carefully designed, it is straight forward to create a paging system.

    My own Veroboard project was designed a good few years back and has 512K RAM, but it is VERY unstable, hence me purchasing the Z80 Playground.

    My Z80 Playground is running a “Real” CP/M 2.2 BIOS. I swap the ROM in and out for WARMBOOTs. I have contacted John and pointed him to my Github and await his response. It can easily be incorporated in to his ROM – I have actually done it. I will make it public on here after John has replied.

    #954
    Phil_G
    Moderator

    >>Yeah I’m aware of the hardware requirements. John’s board would not have to change at all.

    I’m not so sure Steve, Johns ram is enabled whenever rom isnt, so from the external bus, how would you disable onboard ram and rom without modifying the Playground? How would you make a ‘paging hole’ in the Playground memory map? Crucially, yes, the rom is paged out but its replaced by onboard ram – one or the other – theres no option on the standard Playground for that area of the memory-map to be empty, to be filled by external paging. Unless your board has a Z80DMA and you dma into the on-board RAM with busrq? 🙂
    Cheers
    Phil

    #955
    Steve
    Participant

    Okay, having a look at this in more depth. You are correct. Removing the 64K RAM chip will get around the RAM only bit, but then the expansion bus does not pass on the ROM state. It would still be possible to do, but at least one wire would have to be added between boards. Doable, but not so elegant!

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