warren@col.hp.com (Warren Tustin) (04/17/91)
I had some interest in the User port to RS232 interface I built, so I decided
to post the plans. I got the LT1133 as a sample, but I would think it is
available by now. Maybe this will help someone save some money?!
Warren Tustin
warren@col.hp.com
------------------------------------------------------------------------------
Here are the plans for an User port TO RS232 connector using one IC and 4
capacitors. It uses a Linear Technology LT1133 buffer that has 3 RS232
drivers and 5 receivers. It has worked for me with no problems and takes
a minimum amout of wiring to get to work. My board is only the width of
the user port and about 1.5 inches deep in size.
Parts list:
LT1133CN plastic dip or LT1133CJ ceramic dip
RS232 driver from Linear Technologies
(It takes 27mA max (17mA typical) so is well below the 100mA limit of
the user port)
Driver In pins (15,19,21) TTL/CMOS compatible. Unused inputs
| | | should be tied to +5v.
Driver Out pins (5, 7,11) RS232 compatible. Short circuit
protected from -30v to +30v.
Receiver In pins (6, 8, 9, 10,12) Accept RS232 levels (+-30v)
| | | | | and have 0.4v of hysteresis to
| | | | | provide noise immunity.
Receiver Out pins (20,18,17,16,14) TTL/CMOS outputs.
NOTE: Lines above indicate which inputs go with which outputs, and
the pairs can be interchanged freely. I connected them as
described below because the wiring worked out for me the best.
4 - >= 1uF capacitors Used to generate RS232 voltages by a charge pump
technique inside IC
1 1uF capacitor To bypass the 5volt supply for noise rejection.
1 User port female connector. (I just dug this up, I'm not sure
where these can be found, I think it is 0.159" spacing, 24pin.
1 RS232 25pin female connector. Can be found at R-Shack
Some sort of .1" spacing proto board
Connections:
User port connector (Looking into the C64 or C128)
1 2 3 4 5 6 7 8 9 10 11 12
------------------------------------
|XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|
------------------------------------
A B C D E F H J K L M N
Ground & Power:
Pins 1, A, 12, N to Ground of board.
LT1133 pin 2 to pin 2 of User port connector (+5 volts)
1uF capacitor between pin2 and ground (bypass cap)
LT1133 pin 13 to Ground.
RS232 pins 7 & 1 to Ground.
LT1133 capacitors:
1uF from pin 1 (V+) to ground (If polarized (electrolytic) + side to pin 1)
1uF from pin 24 (V-) to ground (As above but + side to ground)
1uF from pin 3 (C1+) to pin 4 (C1-) (Again if polarized, + side to pin 3)
1uF from pin 22 (C2+) to pin 23 (C1-) (Again if polarized, + side to pin 22)
Commodore side RS232 side
User port Signal Pin of Signal Pin of RS232
pin name LT1133 direction LT1133 connector
--------- ------ ------ --------- ------ ---------
B FLAG2 Din 20 <-- 6 3
C PB0 Din connect to above pin 20
D PB1 RTS 21 --> 5 4
E PB2 DTR 19 <-- 7 20
F PB3 RI 18 --> 8 22
H PB4 DCD 17 --> 9 8
J PB5 Not used
K PB6 CTS 16 --> 10 5
L PB7 DSR 14 <-- 12 6
M PA2 Dout 15 --> 11 2
This assumes that you want to connect all of the communication lines. I did
it this way because the C128 programmers reference guide had all of the signals
above listed. If you want to drop RI (ring indicator) you could also use an
LT1134 which has 4 drivers and 4 receivers.
Warren Tustin
warren@col.hp.com