Womble wrote:It originally came with 48K of RAM, the 1st bank is eight 2KB chips, the second bank is four 8KB chips. Both banks are original, but someone has been fiddling. They have cut pin 1 on all 4 of the 8KB chips and wired them together, this they have connected to a 2 way switch on the rear of the machine, flipping the switch will take pin 1on all 4 chips to either logic low or logic high, there is a current limiting resistor in the right place on the switch thankfully. Pin 1 happens to be the Output Enable (called G on the datasheet for some reason).
As it stands I am pretty sure I have a 16KB system with 32KB sitting there comatose. It was neatly done and is very easily undone, am just a bit baffled as to the reasoning behind it.
Womble wrote:Actually I think you are right, oddly enough I have a collection of magazines from the early 80s in binders that show many machines stripped down and it states that this machine has 48KB, but if 16K is video RAM then that would make sense as I have seen other sources say this machine only had 32KB. Certainly only 28KB is available to BASIC, losing only 4KB to the system makes more sense than looking nearly 20KB.
Womble wrote:I have also taken a closer look at the board, pin 1 on all chips was tied straight to the ground plane originally, and I think I took the datasheet too literally. What they call G and refer to as Output Enable is more like Chip Enable (CE) in more modern parlance, the fact "G" appears in the time slice diagrams I think is more to do with chips being enabled or disabled for the sake of paging ram in and out rather than its effect on the read/write cycle.
When the switch is in one position (presumably connecting CE to 5V) the machine will not boot so in that state I would assume the machine has zero RAM.
Womble wrote:Am torn between trying to upgrade the internal RAM to 64K ( I have the right chips lying around ), or trying to track down an expansion card. Trouble is the expansion cards seem to be rarer than rocking horse poo.
Womble wrote:Would you know if a memory expansion card would be useable as RAM for games? I have read that RAM sat on the rear slot or the cart slot will appear as being in a different bank so games may try to directly address memory locations that are not present.
Womble wrote:Have managed to find the schematic/service manual for this beast so I should be able to work out how to add a second 32KB to the main memory. Time to get my head around RAM wiring and addressing I think. Actually have found out that the custom memory controller scans all 4 slots looking for RAM, it chooses the slot with the largest memory and connects the system bus to that slot, in the case of this machine slot 0 is the onboard, slot 1 is the rear edge connector, slot 2 is the cart slot and slot 3 is the synth unit. Will be simpler to build a 64K sram chip onto the rear slot and let the system pick that slot at boot up.
joska wrote:Quite possible. These machines does not have a proper memory management system, so it's up to the individual game to properly detect any expansions.
I would recommend leaving slot 1 and 2 free in case you want to play cartridge based games (like the excellent Gradius/Nemesis games). You don't *need* both slots, but some Konami games has extra features if you combine them. E.g. with Salamander in the cart slot and Nemesis II in the rear slot you'll have a couple of extra planets to explore. Same with the Metal Gear games.
Take a look at msx.org, there's a lot of knowledge in the forums there.
papa_november wrote:I've heard that the CX5M is a sort of MSX1.5, as it has the ROM and RAM of an MSX1 but the VDP of an MSX2. Is this correct?
Womble wrote:I get the impression that the heyday of MSX love is over, the majority of the useful posts on that site point to URLs that are long dead, its a shame as you get an idea of the information that used to exist. Its a good example of why a system specific forum should host their own copies of those files, it saves the whole knowledge base from unravelling over time.
joska wrote:papa_november wrote:I've heard that the CX5M is a sort of MSX1.5, as it has the ROM and RAM of an MSX1 but the VDP of an MSX2. Is this correct?
I don't think this is correct. IIRC the only MSX "1.5" is the Spectravideo SVI 738. The CX5 was released in 1983, which I think is too early for the VDP2.
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