Reset signal duration

By Eugeny_Brychkov

Paragon (1173)

Eugeny_Brychkov's picture

03-10-2020, 08:07

There must be a legitimate source detailing specification of the system reset timing. I am sure I have seen it somewhere, but can not find it (searched in MSX tech data book and in the net). Please help. Thank you!

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By Pentarou

Champion (375)

Pentarou's picture

03-10-2020, 13:52

Reset timing: page 35 of S1985 MSX Engine english Datasheet.pdf ???

By Eugeny_Brychkov

Paragon (1173)

Eugeny_Brychkov's picture

03-10-2020, 22:52

Thank you! This gives us an idea of what the minimal period of the reset signal in application of the S1985 (5.6 us).
But the system recommended, or standardized reset time may differ. I just measured my Yamaha, and its reset deactivates in approximately 230 ms (milliseconds, ~1/4 of second!) after +5V supply goes on.

The actual reset time is defined by the circuit connected to the "reset in" input of the chip. 10 uF and 47 uF capacitors will give very different times.

Z80 datasheet says that minimal reset time must be at least 3 clock cycles (in our case ~ 1 us).

Let me rephrase my question: what is MSX slot standardized reset signal timing? It must be documented somewhere as it is one of the vital properties for the cartridge circuit design.

By Wlcracks

Champion (438)

Wlcracks's picture

04-10-2020, 14:11

I am not sure what you mean by "the" reset timing.
The only |RESET line you can use as an hardware developer is the |RESET output in the expansion slot.
Internally the manufacturer of the hardware will be responsible for a reset and the slowest component will be a factor, but as you state, a capacitor will be the time factor of the reset button. This timing factor will be a factor 100 or more of the time needed to reset the system. I guess the systems without a reset button will have the same like circuit without the button to produce a POR and BOR. The capacitor will have a function to debounce the switch to, and avoid oscillation.
The hardware inserted on the cartridge slot has to respond on |RESET OUTPUT to a negative flank and not to a time due.
Maybe you need a >10 second hardware reset on your new devices, like an option. |reset trigger though negative or positive flanking can do the trick maybe..?

By Eugeny_Brychkov

Paragon (1173)

Eugeny_Brychkov's picture

04-10-2020, 14:24

I need ton know the standard, or guaranteed reset pulse duration on the MSX slot pin 15.

By Wlcracks

Champion (438)

Wlcracks's picture

04-10-2020, 19:17

Eugeny_Brychkov wrote:

... 10 uF and 47 uF capacitors will give very different times...

I think you already gave the answer right there.