HP-IL protocol questions

[J-F Garnier]

(12-27-2019 01:03 PM)grsbanks Wrote:  Question 1: There would appear to be a convention whereby the Accessory ID returned by a device in response to an SAI frame is just a byte of which the upper 4 bits represent the type of accessory (mass storage, printer etc.) and the lower 4 bits a sub-type. Is there any convention regarding what values of the accessory type portion of the AID represent which type of accessory?
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OK, I have an answer to question 1 already thanks to Gary Friedman's "Control the World with HP-IL"

A more complete list is detailed in appendix C.4 of the HP-IL specification (available on MoHPC DVD/USB-key), including the "Analytic Instrument" class (112-127) and the definition of the subclasses.
Regarding the HP-IL ID and AID, not all HP devices comply to these rules, for instance the HP3468 multimeter doesn't answer at all to the SAI (returns the SAI unchanged), it must be searched by its ID="HP3468A" or "HP3468B" depending on the multimeter version! It was a true design flaw in my opinion.
And on the other hand, the HP-82161 cassette drive, the HP82162 printer, and maybe others don't answer to the SDI command, but just to the SAI.

Quote:Question 2: When a talker is sending a series of DAB frames to a listener, the controller can interrupt this process by sending an NRD frame to the talker in place of the echoed DAB frame.
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What happens after the SDA frame if the controller interrupted the process when the talker was sending out the final byte? The controller had no way of knowing that it was the last byte so as far as it knows, the talker still has pending data to send. The talker seeing the SDA frame is going to be in a position where it's supposed to resume sending data but it has no more to send. Does it send another ETO/ETE frame to indicate the end of the transmission or does it just forward the SDA frame back to the controller?

Devices generally are sending an EOT in response to a SDA if they have no (or no more) data to send, this is my recommendation for HP-IL device implementation. But some HP devices (the HP-82166 and the HP82164 interfaces) can just hold the SDA until they get something to send from the interface side. Of course, this locks the loop, potentially forever if no data is received from the interface side.

J-F