From: Baltissen, R (Ruud) (ruud.baltissen_at_abp.nl)
Date: 2003-06-07 09:04:52
Hallo Marko,
My answers are partly based on the IEEE version of PC-Disk.
> 1. Can multiple bytes be sent with ATN asserted?
Yes. The actual cammandcodes are sent with ATN = (L).
> 2. Can the talker and listener change roles when ATN is
> initially deasserted?
No. The controller tells the devices how they have to behave and only the
controller can change that. That a device has to receive and to send bytes
in the same run is just part of the protocol. Just remember the discussion
we had lately about sending the directory under the BASIC-V4 protocol where
so now and then the computer throws in some bytes: the drive has to send and
receive in the same run.
> I remember seeing a piece of code that tells a printer to
> LISTEN and a disk drive to TALK, in order to print a file
> while the computer could do something else.
Quite simple if two drives are concerned:
- you tell the TALKER what file to send [1]
- you tell the LISTENER what file to receive [1][2]
- you tell the LISTENER to start to LISTEN
- you tell the TALKER to start to talk [3]
[1] IMHO the order of these commands is indifferent
[2] The command for a printer will look about the same. Of course it makes
no sence to send a filename. But on the other hand the used channel will
give the printer information about the way to print it.
[3] The command to tell the TALKER to spit its data is only two bytes long.
The fact that they are sent with with ATN = (L) makes the LISTENER to ignore
them.
--
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