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Z80 16 bit i/o [message #8351]

Thu, 25 February 2021 06:51

b1ackmai1er
Messages: 396
Registered: November 2017

Senior Member

Hello,

I was wondering if the capability of the Z80 to use a 16 bit i/o address can be used output a 16 bit data value, like this?

/forum/index.php?t=getfile&id=1993&private=0

/forum/index.php?t=getfile&id=1993&private=0

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Re: Z80 16 bit i/o [message #8352 is a reply to message #8351]

Thu, 25 February 2021 07:06

wsm
Messages: 232
Registered: February 2017
Location: AB, Canada

Senior Member

The short answer is YES, although the instruction is actually "OUT (C),A". Since the actions are fully specified, the Z80 and derivatives actually supply a 16-bit I/O address.

This also works on other members of the Z80 family like the Z180 and eZ80. More importantly some of these other processors require A15-A8 = 0 for internal I/O devices and thus added the IN0 and OUT0 instructions. Zilog's ZDS actually accepts the "OUT (BC),r" form.

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Re: Z80 16 bit i/o [message #8353 is a reply to message #8352]

Thu, 25 February 2021 10:10

cmacarthur
Messages: 26
Registered: April 2018
Location: Alberta / Montana

Junior Member

YES,
You can check out some of Alan's 16 bit I/O z80 boards for the RC2014,
https://hackaday.io/EtchedPixels

https://hackaday.io/project/168355-rc2014-bus-extender
https://hackaday.io/project/170819-16c552-dual-uart-for-rc20 14

They Work GREAT...
you just load BC with 16 bit I/O port address
then out (C),A or whatever register has data byte in it...

The issue is that once you start using/decoding 16 bit I/O, all programs and boards must be changed to 16 bit...
This includes your OS (CP/M etc)

Alan's boards above get around this by only having 1 8 bit I/O location that uses 16 bit addressing...
He swaps the HIGH and LOW bytes on the board (A0-A7 are now high and A8-A15 are now low)...
This also works great for INI,INDR,INIR,OTDR,OTIR,OUTD,OUTI as the "B" reg is INC or DEC giving you block I/O through one 8bit I/O location...

THX
CM

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Re: Z80 16 bit i/o [message #8357 is a reply to message #8353]

Fri, 26 February 2021 01:24

b1ackmai1er
Messages: 396
Registered: November 2017

Senior Member

Thank you. I am keen to try this out Smile

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Re: Z80 16 bit i/o [message #8358 is a reply to message #8353]

Fri, 26 February 2021 07:57

hperaza
Messages: 68
Registered: March 2017

Member

cmacarthur wrote on Thu, 25 February 2021 10:10

you just load BC with 16 bit I/O port address
then out (C),A or whatever register has data byte in it...

I think b1ackmai1er meant 16-bit data I/O and not 16-bit addressing of I/O ports. An interesting idea, that according to his diagram works by redirecting the high I/O address byte to the high data byte of the 16-bit I/O device, and leaving the low address byte for the usual 8-bit I/O port addressing. The only limitation is that it will work only for the output operation; input on the Z-80 is still limited to 8-bits.

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Re: Z80 16 bit i/o [message #8365 is a reply to message #8358]

Mon, 01 March 2021 07:48

cmacarthur
Messages: 26
Registered: April 2018
Location: Alberta / Montana

Junior Member

Sorry Missed that...
YES
The above diagram works great for Output as the high data byte is in the "B" reg

CM

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