Algorythms: OK, but why didn't they just use a 7.16MHz clock then? And how do you know it's devided by 4?

Manuel: Because having a higher frequency xtal devided gives less deviation. As to how I know, it's just from what I have read and heard, and is probably possible to calculate by the amount of cycles an instruction use.

Can the oscilators be changed so msx can be overclocked?

nikodr:

Quote:

Can the oscilators be changed so msx can be overclocked?

Well, 4 or 5 posts up, Algorythms wrote:

Quote:

I have one 32Mhz xtal and one 40Mhz xtal connected with a switch because the 28Mhz one broke. Both increased the speed. With 32Mhz it's devided down to 8Mhz, 40MHz is devided down to 10MHz, which also the benchmark numbers show. 40MHz gives some graphics issues on my tbr in Z80 mode.

I guess that answers your question

Hi,

Regarding MSX turbo R:

The R800 is driven by the 28 MHz crystal which is indeed divided internally to 7.16 MHz. Though, you can take that with a grain of salt because in actual fact, an instruction that takes 1 clock cycle on R800 took 1 M cycle on Z80, which is 4 t-cycles (4 clock cycles) on the Z80. So to make the timing tables simpler (so that they don't have to differentiate between M and T-cycles), they have only mentioned the M-cycles and then said that the CPU runs on7.16 MHz and not on 28 MHz.

The VDP in MSX turbo R has it's own clock crystal at approx. 21 MHz, just like in the MSX2 and MSX2+ models. Though, in MSX2 and MSX2+ models, this 21 MHz is divided by 6 to get the 3.57 MHz clock which feeds the Z80 CPU. So on MSX2 and MSX2+, the CPU and the VDP run perfectly in sync as far as the clock is concerned. On the MSX turbo R however, they run slightly out of sync, because the Z80 and the R800 are both fed from the 28 MHz crystal and the VDP is fed by the 21 MHz crystal.

One consequence is that benchmark programs that measure the CPU speed by counting how many times a certain loop can be done during 1 VDP interrupt cycle, give a slightly different result on MSX turbo R then on other MSX models.


Kind regards,
Alex

Alex, so, we can safely say that it does run on 28MHz?

I put it like this on the FAQ, can you review please?

Quote:

CPU R800 (DAR800-X0G), with 28.63630 MHz external clock and 16-bit ALU. (Can be accelerated to 40MHz by changing the crystal.) Note: the bus frequency is 7.16 MHz, however, an instruction on the R800 that takes 1 clock cycle, often takes 4 clock cycles on the Z80, so one can indeed say that the R800 runs roughly like a 28.6 MHz Z80.

Quote:

I put it like this on the FAQ, can you review please? Quote: CPU R800 (DAR800-X0G), with 28.63630 MHz external clock and 16-bit ALU. (Can be accelerated to 40MHz by changing the crystal.) Note: the bus frequency is 7.16 MHz, however, an instruction on the R800 that takes 1 clock cycle, often takes 4 clock cycles on the Z80, so one can indeed say that the R800 runs roughly like a 28.6 MHz Z80.

Excellent. I have nothing to add.

Nice, This seems to be consistent with the numbers that other users viewed.

Now, is this the correct setting?
It could explain the 21 and 28 thing.

Quote:

Hi, Regarding MSX turbo R: The R800 is driven by the 28 MHz crystal which is indeed divided internally to 7.16 MHz. Though, you can take that with a grain of salt because in actual fact, an instruction that takes 1 clock cycle on R800 took 1 M cycle on Z80, which is 4 t-cycles (4 clock cycles) on the Z80. So to make the timing tables simpler (so that they don't have to differentiate between M and T-cycles), they have only mentioned the M-cycles and then said that the CPU runs on7.16 MHz and not on 28 MHz. The VDP in MSX turbo R has it's own clock crystal at approx. 21 MHz, just like in the MSX2 and MSX2+ models. Though, in MSX2 and MSX2+ models, this 21 MHz is divided by 6 to get the 3.57 MHz clock which feeds the Z80 CPU. So on MSX2 and MSX2+, the CPU and the VDP run perfectly in sync as far as the clock is concerned. On the MSX turbo R however, they run slightly out of sync, because the Z80 and the R800 are both fed from the 28 MHz crystal and the VDP is fed by the 21 MHz crystal. One consequence is that benchmark programs that measure the CPU speed by counting how many times a certain loop can be done during 1 VDP interrupt cycle, give a slightly different result on MSX turbo R then on other MSX models. Kind regards, Alex

Quote:

Quote: I put it like this on the FAQ, can you review please? Quote: CPU R800 (DAR800-X0G), with 28.63630 MHz external clock and 16-bit ALU. (Can be accelerated to 40MHz by changing the crystal.) Note: the bus frequency is 7.16 MHz, however, an instruction on the R800 that takes 1 clock cycle, often takes 4 clock cycles on the Z80, so one can indeed say that the R800 runs roughly like a 28.6 MHz Z80. Excellent. I have nothing to add.

Apart from taking out the word "often"?