Amstrad CPC464: Part 4 (6128 firmware)
11The best of both worlds! Okay, I'm biased ... we had a 464 with green screen growing up so I have fond memories of the 464 ... even being teased at school because the 464 had a coloured keyboard ... weird, huh? ;)
But I definitely prefer it still over the 6128 ... I think the 464's keyboard layout is better (less cramped), it has a built in datasette/datacorder (retro tapes keep coming out) and Mr Zaxon builds his DDI-4 and DDI-5 interfaces exclusively for the 464.
However ... the 464 has some limitations, even if you expand its memory.
The 464 has BASIC 1.0 whereas the CPC664 and CPC6128 have BASIC 1.1.
But there are still differences in the firmware between the 464/664 and the 6128 ... I'm guessing routine entry addresses sometimes are different ... ?
The ROM (40009) used in all machines is 32KB ... replaceable by a 27C256. Depending on your 464 board, pin 1 is either unconnected or is connected to ground.
You can replace this with a 64KB ROM (27C512) which has the 464 firmware & BASIC 1.0 in one 32KB segment, and the 6128 firmware & BASIC 1.1 in the other 32KB segment.
In this case pin 1 is the A15 address pin.
Why would you want to do this, instead of just switching to 6128 permanently? Well, maybe there's some ancient software (or demos) that only work on the 464 ... hey, simply switch back to 464 mode.
First ensure that your pin 1 is not connected to ground - in my case it wasn't, but other boards it is so you need to cut the track.
Then I connect a SPDT switch ... the common goes to pin 1 (A15) and the two throws are connected to 5V and GND ... so A15 will be high or low, selecting the lower or upper 32KB ROM.
A good test is Sid Meier's Pirates for the Amstrad. As per Amstrad Action issue 32 (May 1988), p45, this game is for the 6128 only, regardless of memory expansion ... this hints that it uses 6128 firmware address (or something).
I confirmed that a 464 with Zaxon's DDI5 and the 6128 firmware will indeed run Pirates! ... with the original 464 firmware, it crashes.
I also switched this UK-sourced 464 to "Aussie mode" by connecting LK1 and LK2 ... this changes the company name from AMSTRAD to "Awa" ... which is incorrect ... it should be "AWA", standing for Amalgamated Wireless Australia (I might patch the ROM again to fix it), but this is what Aussie-bough Amstrads displayed on boot.
Zaxon's DDI4:
https://www.sellmyretro.com/offer/details/32790
Zaxon's DDI5:
https://www.sellmyretro.com/offer/details/36061