MSX HDMI mutlimedia card

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By Daemos

Paragon (1672)

Daemos's picture

26-03-2014, 13:37

On turbo R the clk signal of the slot indeed reads 3.58 MHz. On upgraded machines this signal gets clocked up to the turbo frequency. I have not been able to decipher what happens on the turbo MSX2+ machines due to lack of data.

I don't know what happens to the bus frequencies of the slots. It propably is the same as the CPU on the turbo machines but I don't know what happens on the turbo-R.

If you really like to know for sure, ask Eugeny or Alwin (Retrotechie). They know all these things for sure. I am actually curious myself as well so i hope you will post the answer when you get them.

By maxis

Champion (512)

maxis's picture

26-03-2014, 14:00

Daemos wrote:

I have not been able to decipher what happens on the turbo MSX2+ machines due to lack of data.

If you really like to know for sure, ask Eugeny or Alwin (Retrotechie). They know all these things for sure. I am actually curious myself as well so i hope you will post the answer when you get them.

Thanks.

I had the same problem with MSX2+, since I do possess none. So far, I've experimented with the machines based on S3527, S1985 and 1990 engines. They all behaved as the spec. But reading the forum, I felt like many in turbo mode experienced the pitch shift of SCC. I was trying to understand why is that.

But Grauw and Manuel precised when it happens. So, any "official" machine should respect the spec and the bus timing therefore.

In my case I use 3.57 slot clock and RESET to synchronize the internal VDP to mine in the cartridge. However, there is no guarantee, that these 3.57 come from the VDP's 21MHz oscillator.

In a future, I should anyway replace the write-only VDP access by full r/w access on a different group of ports (0x88-0x8B). This is also advantageous since there will be no waitstates generated by the MSX engine.

By Meits

Scribe (5650)

Meits's picture

26-03-2014, 18:42

A panasonic MSX2+ doesn't pitch shift SCC. Only PSG goes up in turbo mode.

By Grauw

Ascended (8515)

Grauw's picture

26-03-2014, 18:51

Meits wrote:

A panasonic MSX2+ doesn't pitch shift SCC. Only PSG goes up in turbo mode.

Ha, so the cartridge output clock does not change, but the internal clock to the PSG does. That’s odd! Smile

By Pencioner

Paladin (993)

Pencioner's picture

26-03-2014, 20:43

It seems that PSG and CPU are on MSX engine single chip, and you cannot divide the internal clock, hence the external connectors get the clock divided by some schematics outside the engine chip (like, without turbo mode the clock goes directly from MSX engine to pin on cartridge slots, with turbo mode it gets routed via the frequency divider). Just opinion, but i'm pretty sure the reason is like that.

By maxis

Champion (512)

maxis's picture

27-03-2014, 01:00

Pencioner wrote:

It seems that PSG and CPU are on MSX engine single chip, and you cannot divide the internal clock, hence the external connectors get the clock divided by some schematics outside the engine chip (like, without turbo mode the clock goes directly from MSX engine to pin on cartridge slots, with turbo mode it gets routed via the frequency divider). Just opinion, but i'm pretty sure the reason is like that.

Fully agree. What I see on A1-ST and also from Hand Otten's schematic pages is that T9769 has no clock output, only the clock input. Also on the first page of A1-WSX there is a pinout of the 6140140 PLA. There we can see two clock inputs from the VDP : DHCLK=10.74MHz and CPUCLK=3.57. And the clock output going to the MSX engine is switchable between CPUCLK & DHCLK/2. And another clock CLK4=3.57MHz going to the SLOT.
As you mentioned, there is an external to the MSX engine circuitry which manages the flipping from one clock to the other. I'm assuming the same and this is done inside that PLA.

One more comment:
DHCLK and CPUCLK are phase synchronized, where one CPUCLK period is exactly 3xDHCLK periods. Then, likely by generating inside PLA the waitstates to MSXENGINE, the required slow timing diagram can be achieved in TURBO mode matching the original Z80 running at 3.57MHz.
Then, possibly, the small timing difference in TURBO vs NONTURBO observed on the MSX SLOT can be compensated inside the PLA by phase shifting the CLK4 output.

So, for the moment, I'll stick to the MSX datapack thing.

BTW, interesting to know how many machines were produced with the native TURBO mode?

By stefA

Rookie (26)

stefA's picture

27-03-2014, 20:48

Wow! I missed this thread, it seems....
Please count me for a fully assembled one!
Cheers
Stefano

By maxis

Champion (512)

maxis's picture

27-03-2014, 22:51

stefA wrote:

Wow! I missed this thread, it seems....
Please count me for a fully assembled one!
Cheers
Stefano

Ok +1 assembled.

By zPasi

Champion (474)

zPasi's picture

29-03-2014, 09:18

Count me in too. I was thinking pre assembled (smd parts) one but looks like there are't many other than smd parts anyway... So I guess fully assembled it is.

And, I assume the sources are or will be available, so we can hack this thing when we've got it?

By HDCORP

Rookie (17)

HDCORP's picture

29-03-2014, 10:06

Count me in too

assembled model one

thanks

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