Rombo Redux ROMboard now Plus compatible

Started by The Equalizor, 01:24, 04 January 22

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The Equalizor

Hi Everyone,

As people really seem to like this board I thought I'd announce that I've found the issue that was causing Plus machine incompatibility, so moving forward all boards will have this fix and work on both CPC and Plus machine with the addition of a 50 Way Centronics connector or a Centronics Adaptor.

I've also managed to finally source the Centronics 50 way connector at a reasonable price so the Plus versions will cost the same as the Standard version while this connector is available at the better price.

If anyone wants one of these boards, please, PM me.

Cheers

Rob

Cwiiis

Out of interest, what was the issue?

RetroCPC

#2
From my understanding, a too weak 1k pull-up resistor was fitted (ROMDIS line)?, replaced with 680 ohms...

The Equalizor

Yup, that was exactly the issue. Due to a mistranslation between my schematic designator and the PCB the 680 ohm resistor went over as a 1k on the silkscreen. This was fine for the CPC but not for the Plus.


Regards


Rob

RetroCPC

#4

I often catch myself making the same mistake - the default resistor on my schematic entry is 10K  - too easy to forget to change to the actual resistor value...

Really the default value should be "X" to prevent such potential mistakes...

To be honest. normally 1K would be plenty OK for a pull up resistor... but the "Tri-State / Active pull down" being achieved with the aid of a diode on the ROMDIS line...

Would be guessing that the CPC+ is CMOS level sensitive on the ROMDIS line, while the earlier CPC's are TTL logic level based.

Bryce

Quote from: RetroCPC on 19:59, 09 January 22
I often catch myself making the same mistake - the default resistor on my schematic entry is 10K  - too easy to forget to change to the actual resistor value...

Really the default value should be "X" to prevent such potential mistakes...

To be honest. normally 1K would be plenty OK for a pull up resistor... but the "Tri-State / Active pull down" being achieved with the aid of a diode...

Would be guessing that the CPC+ is CMOS level sensitive on the ROMDIS line, while the earlier CPC's are TTL logic level based.

Even the powersupply that's being used can make a difference. On one supply a 680R may work and with a different supply it may not work. That's why it's always best to match pull-ups to the device you're interfacing to.

Bryce.

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