Re: HPIB bus commands

From: Marko Mäkelä (
Date: 2004-04-19 10:23:22

On Mon, Apr 19, 2004 at 12:45:47AM -0700, Larry Mollica wrote:
> One interesting tidbit, the OPEN statement allows 4-31 as IEEE488 
> addresses, with 0-3 used for PET internal devices. But we found (ok, 
> by accident), that you can address IEEE488 addresses below 4 by using 
> values over 31, like
> OPEN 1,34
> to talk to IEEE488 bus address 3.

Wouldn't that access device 2 (32+2=34)?  On the Commodore serial bus,
the device number is simply ORed with the bus command.  I doubt that
the TALK command (e.g., GET# or INPUT# from the file) would work with
a device number in the 32..62 range.  On the Commodore 64, typing
LOAD"FILE",88 locks up the computer.  (That's device number $58 hexadecimal.)

BTW, there is some magic in the high-order bits of the file number, and
possibly device number.  One of them controls CR to CR/LF transformation,
and setting another bit avoids sending the secondary address, if I remember
correctly.  This is on the Commodore serial bus; I haven't disassembled the
PET firmware.


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