Man overboard!!!

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

For anyone who's wondering, "Motorola bus interface" could mean two things, both distinct from the Intel approach. The Motorola 6800 bus matches that of the 6502, but the Motorola 68000 bus is something else entirely. I remember getting momentarily tripped up by this ambiguity, perhaps in a datasheet from NXP; I don't recall.

[Edit:] Integer multiples of the exact rate do eliminate error, but 10X 1.8432 MHz isn't the only option -- you can go 3X or 5X the 1.8432 MHz, for example, and still have zero error.

BTW and FWIW, the SC16IS750 I'm playing with accepts rates up to 80 MHz on its 16X input clock. At that rate you get pretty fine resolution, so even if the math won't allow you to get your exact desired rate, you're bound to have an error that's darn small. A degree of error is tolerable anyway, as Garth noted. But running a higher input clock lets you do slightly better, FWIW.

I don't find your meaning clear, I'm afraid. Any chance you can post an up dated schematic, please?

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Right you are; I should have clarified that. The "Motorola bus" in this case means the 68000, not 6800, something that NXP doesn't explicitly state in the data sheets.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

Sure.



Looking at the VIC-20 schematic again I was incorrect to say the expansion address is only valid when Φ2 is low. I still don't know why the original circuit doesn't work.

Thanks. What are you using as a reference for the VIC-20 signals -- can you post something, or provide a link?

Neither do I, but we know Andrew's circuit which you linked to does. That was your starting point, but it failed. The explanation probably has to do with what the VIC-20 puts between its 6502 and the expansion port.

Footnote to the logic-level discussion: your original circuit should've used 74HCT00, not 74HC00. But it's not the sort of mistake that guarantees failure. Sometimes stuff that shouldn't work does. (Erratically, perhaps.)

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

I use this schematic (or an original paper version of it) http://www.mainbyte.com/vic20/e_schematic.pdf along with various paper and PDF books (VIC-20 Programmer's Ref, Vic Revealed).

IO2 you connect to ~CS2 is,gates with PHI2. I would rather connect ~CS2 to ground. It is sufficient to have dedicated RD and WR to select the device.

Thanks for the suggestion I'll give it a try.

Could the terminal be transmitting a continuous break character when there is nothing else to transmit ?
Would it be necessary to have to filter out break characters in the receiver ?
(Assuming there's no CTS/RTS hookup).

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http://www.finitron.ca

I've now got the board stable at 9600 now. The driver code is nearly complete, just need to handle dropping RTS when the receive buffer is nearly full. I did have some problems with the MODEM Control Reg, reading it doesn't seem reliable, sometimes bits seem to flip which causes problems when toggling the LEDs I've attached to /OUT1 & /OUT2. I've used a zero page byte to store the authoritative state. No other register, including the Scratch Reg seems to suffer from this.