Message-ID: <1655@iddic.UUCP>
Date: Mon, 30-Apr-84 22:16:06 EDT
Article-I.D.: iddic.1655
Posted: Mon Apr 30 22:16:06 1984
Date-Received: Fri, 4-May-84 02:46:31 EDT
Organization: Tektronix, Beaverton OR
Lines: 19

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.

Message-ID: <305@ihuxu.UUCP>
Date: Fri, 4-May-84 09:46:53 EDT
Article-I.D.: ihuxu.305
Posted: Fri May  4 09:46:53 1984
Date-Received: Sat, 5-May-84 01:28:42 EDT
Organization: AT&T Bell Labs, Naperville, IL
Lines: 27


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