Re: ATN questions on the serial bus

From: Marko Mäkelä (
Date: 2003-06-10 18:41:15

The following message bounced due to unregistered address.  I removed
quoted-printable encoding from it and rewrapped lines to less than 80
characters.  André, I agree with you on both topics: the drives lack
the hardware to assert ATN, and HTML mail is a bad thing, even if using
an HTML-capable mail user agent.

One more thing is that the C64 and VIC-20, maybe other computers as well,
may leave CLK or DATA in the active state when the bus is idle.  So,
in order to connect multiple controllers on the serial bus, you will have
to enter some POKE commands to make the signals really idle.

(who goes back to debug his serial bus receive routines on the C2N232)

From: "Andre Fachat" <>


let me tell you, neither the CBM parallel disk drives, nor the serial IEC
disk drives
are capable of changing the ATN state. So the C64/PET is essential to start
the transfer (otherwise you could send the drive a command to spool to the
printer, and it could by itself tell the printer to listen.)
However, with the C64/PET always being the controller, it can actually always
interrupt any transfer on the bus by making ATN active. All devices then
break from their transfer and await the command.
This "one controller" design makes it difficult for multiple PETs sharing
a common disk drive. The users always have to "synch manually" about who can
use the bus/drive.


P.S.: off topic: what about HTML mails. They are difficult to read with a
text based mailer or my internet mail providers web interface...

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