Can you slow down EPROM access time? UPDATE: AT28C256 is worse!?

[HB9EVI]

well, the AT28C256 has a read access time of 150ns; so at about 6.6MHz clock rate it'll be too slow
ans my guess would be, it's not going to be different with the other ones named here in the thread

[m k]

Manual offers 8 and 12MHz oscillators /2 for clocks.

How it goes, first ALE and a bit later CE/OE and then next clock reads?

If CE/OE is next clock then 3rd clock reads.

[Rat_Patrol]

I do have some NOS chips on order, will see if those work.

I also bought some (probably counterfeit, who knows) n80C196kb chips from Aliexpress, and to my amazement they worked fine with the new ATMEL eproms! The date code on these Chinese chips are 2003. So that was interesting.

[james_s]

what clock speed is the system running at?

I'm using an AT28C256 on my Z80 board clocked at 6.144MHz - and that's working reliably

12MHz, regulated internally by the 80c196KB

I just looked at the datasheet for the 80c196KB and it shows it as using an external crystal. "Regulated internally" suggests an internal RC oscillator which this part does not appear to have.

If the microprocessors work at all they are very unlikely to be counterfeit. They're probably just surplus parts.

[Rat_Patrol]

what clock speed is the system running at?

I'm using an AT28C256 on my Z80 board clocked at 6.144MHz - and that's working reliably

12MHz, regulated internally by the 80c196KB

I just looked at the datasheet for the 80c196KB and it shows it as using an external crystal. "Regulated internally" suggests an internal RC oscillator which this part does not appear to have.

If the microprocessors work at all they are very unlikely to be counterfeit. They're probably just surplus parts.

There is only 1 external crystal, and it is on the opposite side of the board feeding a processor. Unless the 80c is getting a clock signal from it, the datasheet I read shows internal 12Mhz operation, which makes sense with the board.

So far, my Chinese micros have been 100% (small sample size of about 15 right now, going through testing), so I'm a happy camper there.

[CaptDon]

6.144mhz, that's a blast from the past!!! I bought a real Intel SDK-85 kit and that is the frequency they run the 8085 at. I think that frequency divides down perfectly for hardware UART clock generation but the SDK-85 monitor program used the SID and SOD pins as a software UART. I did successfully get my software UART timing loops to work perfectly at 4800-8-N-1 to decode NMEA strings and transmit test strings. 4800 was the limit however for the ability to do a soft UART. At 9600 you just can't get the timing close enough to be reliable. 2 no-ops is too long, 1 no-op is too short, etc.! I also re-wrote the monitor program to run the 8251 hardware UARTs. That makes for a much better system!! Those SDK-85 and SDK-86 units bring a fortune on Ebay. I have built at least 5 cloned units and even wrote my own tiny monitor from scratch!! Probably around 600 bytes!!!