Wirin' up blinkenlights

From: Eric Smith <eric_at_brouhaha.com>
Date: Tue Jun 13 00:48:40 2000

ard_at_p850ug1.demon.co.uk (Tony Duell) wrote:
> IIRC an EPP port gives you 8 data lines, which is no way enough to talk
> to an 11/45 front panel (there are 18 data/address input switches, 18

EPP gets you eight data signals, a R/W* line, an address strobe, and
a data strobe. It's equivalent to a multiplexed-address-and-data
peripheral bus. So you can hang basically as many I/O signals off it
as you're willing to wire up.

There's even a signal that can be used as an interrupt input.

The nice part is that the "SuperIO" sort of chipsets do all the handshaking
for you, so if you want to write a 0x32 to EPP device register 0x2a, all
you have to do is two write cycles. No bit-banging of the control lines
or handshake inputs required.

It's pretty handy. The only annoying part is the need for the EPP device
to generate a transfer acknowledge signal. I would have been slightly
happier if they spec'd a standard default cycle time, and required the
peripheral to assert a wait signal if it couldn't complete the transfer
that quickly. That would allow for very simple devices with less logic.
Received on Tue Jun 13 2000 - 00:48:40 BST