using a PC serial port to control old logic ICs and shift registers

[rob77]

Is it practical to use the serial port of a computer to send data to shift registers like that

Um.  No.  You can shift the voltage levels easily enough, but shift registers require a clock signal to shift the data in from their data input, and a PC's "async" serial port does not provide such a clock.  Deriving such a clock from the bit pattern on the serial port is complex enough that the easiest way to do it these days probably involves a small microcontroller.  (That'd be a nice little project, too.  6 or 8 pin microcontroller, one input (async serial, clamped from rs232 voltages, autobauded async serial, two outputs: clock and data.)

let me slightly disagree basically i agree with what you wrote, but i disagree with the statement it's complex... have look at the DASA programmers for AVR. the ISP programming interface is data and clock - and it's driven easily by the PC's serial port. you can't achieve high transfer speeds and low jitter on the clock, but it's pretty usable up to some speeds.
for higher speeds the micro is the way to go - as you suggested.

[David Hess]

The DASA interface just bit-bangs the RS-232 port without using the asynchronous transmitter or receiver.  4 lines are used for one synchronous clock output, one data output, one data input, and one reset output.

Used this way, the RS-232 port is not going to be any faster than bit-banging a parallel port.

[rob77]

The DASA interface just bit-bangs the RS-232 port without using the asynchronous transmitter or receiver.  4 lines are used for one synchronous clock output, one data output, one data input, and one reset output.

Used this way, the RS-232 port is not going to be any faster than bit-banging a parallel port.

yes exactly, no-one says ot will be fast but my post was a reaction to the

"and a PC's "async" serial port does not provide such a clock."

.