24 Jun
2013
24 Jun
'13
7:09 p.m.
On Jun 24, 2013, at 5:59 PM, Jim Brain wrote:
I should probably not sound so authoritative, since I
am sure something used the lines.
But, since I was intrigued, I popped open a VIC1101A RS232 cart, and it pulls the + phase
of the 9VAC, rectifies it via single diode, cleans it up with a cap, and uses that for +
on a 75188/75189 pair (1488/1489 compatible, I presume).
The (-) leg is more interesting. It looks like it is created on the cart via a RC
circuit, a B562C PNP and a small transformer from the 5V supply.
Weird setup, since I thought the VIC1101A was from the VIC-20 era, where the -9V would be
easily available on the user port.
There's a story behind that.
I thought one other thing that the 9VAC was used for on the 8-bit Commodores was to supply
a clock signal for the TOD clock on one of the CIAs, but I might be mistaken.