Shift Registers as Delay Lines (was Delay lines in TV sets) - test-drb@ccmp.vtda.org

17 Dec 2007

...

Subject: Shift Registers as Delay Lines (was Delay lines in TV sets)
   From: "Rick Bensene" <rickb at bensene.com>
   Date: Mon, 17 Dec 2007 15:06:38 -0800
     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>

Tom Watson wrote: 
> If you decide to make up a delay line to hold CPU data, try a 
> prototype using shift registers.  They are a bit easier to 
> make up, and often the chips are available.  The problem is 
> that they come in weird (at times) sizes (132, 80, and the 
> like).  I'll leave it to the reader to determine the 
> usability of odd sizes and their original use.
>  

Msot of those are later designs and tended to be for line printer,
CRT and other displey and printing systems.  Common sizes for that
were line printer 132, CRT 80 and 72 (tty was 72!) and the true 
oddball lengths were the 1024, 224, 192 and 56. 

MOS shift registers of lengths greater than a few bits are very late 
60s (after 67 or so). By early 70s parts 1024 long ere not uncommon.

What makes them interesting is you can use them word or digit parallel
and very deep by cascading them serially.  For lesser registers older 
4 and 8bit TTL devices in parallel can be very effecive in providing 
a digit wide by 8 digits deep register in a small space.  This is 
truely getting into late 60s early 70s serial compurer design right
on the cusp of the days of the last serial drums or disks for local
store and the drums would then be for the larger program store.

Allison

...
 A lot of early MOS shift registers were developed
specifically for use
in electronic calculators, as solid-state replacements for magnetic core
memory or magnetostrictive delay lines.  Since most all electronic
calculators in the mid-'60's through the late 70's operated in BCD or
some alternate four (or sometimes five)-bit representation of decimal
digits, the shift registers were usually made with a number of stages
that was a multiple of four or five, with a few extra bits here and
there for timing and synchronization.  That's why many of these devices
as an unusual number of stages.  In some calculators from the late
'60's, as IC logic had pretty much replaced discrete transistor designs,
there were different versions of the same machine, earlier machines
which used a magnetostrictive delay line, and "updated" versions which
dispensed with the delay line, and replaced it with a number of MOS IC
shift register devices.  Functionally, the machines were identical. As
far as the digital logic section of the machine went, also identical.
The only real changes were the removal of the read amplifier and write
driver for the delay line, and replacement with some simple
level-shifting and power supply circuitry to properly drive the shift
register chain.

Rick Bensene
The Old Calculator Museum
http://oldcalculatormuseum.com 