garyh@iddic.UUCP (05/01/84)
Subject: RS232 H/W question
Newsgroups: net.micro.cbm
...
Does anyone know what's in Commodores RS232 cart? I am using a homebrew RS232
board which (unfortunately) has an external power supply for +/- 12V. How
(exactly) do they get the driver voltages from the +5DC and/or 9VAC? I know
that the trash-80 model 1 RS232 uses an
ASTEC module that takes in +5 and puts out +-12, but a photo of Commodore's
board shows only one (or so) other chips besides the line drivers/receivers.
Any help would be appreciated.
Gary Hanson
{ allegra,decvax,..others..} tektronix!iddic!garyh
Dear Lisa and Mac: Sorry, but no mice allowed in my house; that's why I have
a cat. Also, if I want icons, I'll go to church. If I hear 'user friendly'
one more time, I'm gonna puke.russell@ihuxu.UUCP (Larry Russell) (05/04/84)
I have just built an RS232 card myself for the C64. To get the +12V
is easy; if you have a "Programmer's Reference Manual," look at the
schematic to see how they do it: use a VM08 (or equivalent) full-wave
bridge (Radio Shack) across the 9VAC leads, ground the negative output
of the VM08, and put a 220 microfarad electrolytic capacitor between
+12 (the VM08 + output) and ground.
No voltage regulator is needed as the voltage is not critical and the
ripple is not bad for the amount of current you need.
To get the -12V you must AC couple to the 9VAC leads; connect the AC
inputs of another VM08 to 9VAC through 220 microfarad capacitors.
The positive terminals of both caps are connected to 9VAC; the negative
terminals to the VM08. Put another 220 mfd capacitor across the VM08
output and this time, of course, ground the VM08 + output.
GND
+ - ___________ | + -
9VAC------|(---------|~ +|--------|----|(---+
| VM08 | |
9VAC------|(---------|~ -|------------------+--> -12V
+ - |_________|
Larry Russell
AT&T-BL
Naperville, IL
ihnp4!ihuxu