stephenc@tekgen.UUCP (Stephen Coan ) (08/20/86)
()
I designed an adaptor to convert the TTL levels on the User Port to true
RS-232 levels a number of years ago. This has worked very satisfactorly
not only on my Commodore equipment, but also other micro-processor projects
that I have built. The nice thing about this is that it will generate the
required negative voltage for the RS-232 signal lines without special
hardware. The whole project takes 3 ICs, 2 diodes and 4 capacitors. It
incorporates all the RS-232 signals that are present in the Commodore User
Port so should be compaitible with most all RS-232 devices.
Two possible cable terminations are shown on the schematic. One is for
a DTE type device (Data Terminal Equipment) which would be used when the
Commodore is used as a terminal. The other is DCE (Data Communications
Equipment) and would be used when the Commodore is the computer end of the
RS-232 line. Just fold the schematic so the DCE overlays the DTE to see
what is changed between the two types. DTE is usually a Male Pin connector
while DCE is usually a Female Pin connector.
If you look at the generated DC levels to the 1488 chip, you will notice
quite a bit of ripple. This is OK in that the valley never drops below
three (3) volts which is the required minimum level for RS-232.
The ASCII graph schematic that follows has been checked and is accurate.
I hope that this is useful for those who are looking for a RS-232 adaptor.
Schematic Follows --------------------------------------------------
USER PORT STD. DTE OPT. DCE
CABLE CABLE
| +------\ | |
| 2 | \ 3 | |
M -|------------------| U1-A O-------|- 2 TX ----------|- 3 RX
| | / | |
| +------/ | |
| \ | |
| | \ | |
| 3| \ 4 4+------\ | |
O -|---|U3-B O----+---| \ 6 | |
| | / | 5| U1-B O-------|- 4 RTS ----------|- 5 CTS
| | / +---| / | |
| / +------/ | |
| | |
| \ | |
| | \ | |
| 5| \ 6 9+------\ | |
E -|---|U3-C O----+---| \ 8 | |
| | / | 10| U1-C O-------|- 20 DTR ------+---|- 6 DSR
| | / +---| / | | |
| / +------/ | | |
| | | |
| | | |
| / | | |
B -|---+ / | | | |
| | 3 / | 1 | | |
C -|-----------------O U2-A -----------|- 3 RX ------|---|- 2 TX
| \ | | | |
| \ | | | |
| \ | | |
| | | |
| | | |
| | | |
| / / | | |
| / | / | | | |
| 10 / |11 6 / | 4 | | |
L -|----O U3-E ------O U2-B -----------|- 6 DSR ---+ +---|- 8 DCD
| \ | \ | | | |
| \ | \ | | | |
| \ \ | | |
| | | |
| | | |
| / / | | |
| / | / | | | |
| 12 / |13 8 / | 10 | | |
K -|----O U3-F ------O U2-C -----------|- 5 CTS ---|------|- 4 RTS
| \ | \ | | | |
| \ | \ | | | |
| \ \ | | |
| | | |
| | | |
| / / | | |
| / | / | | | |
| 8 / | 9 11 / | 13 | | |
H -|----O U3-D ------O U2-D -----------|- 8 DCD ---+------|- 20 DTR
| \ | \ | | |
| \ | \ | | |
| \ \ | |
| | |
| | |
N -|-----------------------------------|- 7 SIG GND ----------|- 7
| | |
| +5V | |
2 -|----+------------+ +------|- 1 PROTECTIVE GND --------|- 1
| | | | | |
| | | | | |
| --+-- 0.1uF | ------- | |
| --+-- 10V | --- | |
| | | - | ***********************************
A -|----+ | | * *
| | | | * U-1 1488 RS-232 XMTR *
| ------- | 14 +----+ 7 | * *
| --- +----| U2 |--+ | * U-2 1489 RS-232 RCVR *
| - | +----+ | | * *
| | | | * U-3 7404 HEX INVERTR *
| | 14 +----+ 7| | * *
| +----| U3 |--+ | * DIODES SIGNAL DIODES WILL *
| |\ | +----+ | | * WORK HERE *
| | \| | | * *
10-|----| |---+--------+ | | * NOTE: THE RS-232 VOLTAGE *
| | /| + | | ------- | * BE APPX +/- 6 VOLTS *
| |/ | --+-- | --- | * WHICH IS OK TO USE *
| 100uF --+-- 14 | - | * PER RS-232 STANDARD *
| 15V | +-----+ | * *
| | | | 7 | * *
| ------- | U1 +----+ | ***********************************
| --- | | | |
| - +-----+ | |
| 1 | ------- |
| | --- |
| 120uF | - |
| 15V | /| | | ***********************************
| +|| |/ | | | * *
11-|--||----+---| |----+----+ | * Commodore User Port to RS-232 *
| || | |\ | | | * Adaptor designed by Stephen *
| | | \| | | * Coan, Version 2, 03-NOV-83. *
| | | | * *
| -------- 100uF ---+--- | * This general design has also *
| \ / 15V ---+--- | * been used in other devices *
| \/ + | | * where a negative voltage was *
| -------- | | * not available for the RS-232. *
| | | | * *
| | | | * NOTE: The DTE is usually a *
| +-------+----------+ | * male pin DB-25 connector and *
| | | * the DCE is usually a female *
| | | * DB-25 connector. Overlay the *
| ------- | * DCE over the DTE to see the *
| --- | * connection scheme for DCE *
| - | * usage. *
| | * *
| | ***********************************
| |
| |