HP82165 GPIO->HPIL handshake

[cmurillo]

Greetings to all...

My name is Carlos E. Murillo-Sanchez and in the past I have toyed with my hp calculator/instrument collection quite a bit, though in recent years I've had to leave hobbies mostly aside due to work (sad). I have several 71Bs, 75's, 41's (these require some TLC right now), a 67, a 97, and a series of peripherals including HP9114B, HP82143, HP3468, HP3421 (2 of them), HP82165, HP82166, and quite a few more.

Now on to my question...

Lately, I wanted to make a quick and dirty addition to the HP82165 in order to implement 16 bits of opto-isolated digital I/O . I would like to change only minimally the default power-on configuration of the HP82165, so I want to stick to negative handshake logic. The output part was easy, though I did have to issue the configuration commands

A = DEVADDR("HP82165")
SEND UNT UNL MTA LISTEN A DDL 0 DATA 64,0,220 UNT UL
ENDLINE ""

This essentially changes the 8 bit data mode to 16 bit. Afterwards, a command such as

OUTPUT A; CHR$(255)&CHR$(255)

or

SEND UNT UNL MTA LISTEN A DATA CHR$(255),CHR$(255) UNT UNL

succesfully writes 1's to two HCT373 latches strobed by a negated DAVO signal; the RDYI and DACI handshake lines are connected to ground.

However, reading has proved not so simple. I have a couple of LS245's connected to the DA and DB buses (easier to wire than 244's) and when their enable G_ goes down they allow the external data into the DA,DB buses. I have tried the following handshake options:

1) Feed RDYO back into DAVI and also towards the G_ input in the 245's . Reading from the HP82165 using an ENTER A;C$ command results in hung HPIL bus.

2) Connect DAVI to ground and RDYO to the G_ input in the 245's. Results in a hung HP82165 on power up.

3) Lastly, an HCT74 was used as follows:
-RDYO is negated and then fed to the CLK input in the flip-flop
-The D input of the flip flop is fed a logic 1, so a positive transition in the CLK sets the flip flop
-The Q_ output of the flip flop is fed to DAVI
-The DACO handshake is fed to the CLR_ input in the flip-flop.

I tried to show this in an ASCII text diagram but the spacing gets lost.
_____ ________
| 1-| D |
RDYO |------- |>o------| CLK |
| | |
DACO |----------------- | CLR_ |
| | |
DAVI | ------------------|Q_ |
_____| | |_______|
|
|_________> To enable G_ in HCT245 transceivers

This arrangement also results in an HPIL timeout when reading from the HP82165.

I would like to derive the handshake directly from the RDYO, DACO signals, without having to develop an external clocked logic for this. I would also like only minimal configuration changes to the default power-on settings in the HP82165.

Can somebody tell me what I am doing wrong?

Regards,

Carlos E. Murillo-Sanchez.