Carbolite MTT 12/38/850 - Manual (Page 4)

MTT
4
MF38 – 3.07
2.3 Connection to a Computer
This furnace is normally fitted with RS485 3-wire communications on the main controller only.
For information, RS232 and 5-wire connections are also shown below. This section does not apply
if the digital communication facility is not fitted.
If the RS232 option is supplied, then the furnace is fitted with one subminiature D-socket
connected to the controller comms module. RS232 is suitable for direct connection to a personal
computer (PC), using a “cross-over” cable as follows (the linked pins at the computer end are
recommended but may not be necessary). The cable is usually 25-pin at the furnace end and 9-pin
at the computer, but other alternatives are shown in parentheses.
Furnace end of cable RS232 Cable: furnace to PC Computer end of cable
female 25-pin (9-pin) 9-pin (25-pin) male
Tx 2 (3) 3 (2) Tx
Rx 3 (2) 2 (3) Rx
Com 7 (5) 5 (7) Com
7,8 (4,5) Link together
1,4,6 (6,8,20) Link together
If an RS485/422 option is supplied, then the furnace is fitted with two D-sockets. Connection
between products is by “straight” cable as follows:
RS485 cable: furnace to furnace
female 25-pin (9-pin) 25-pin (9-pin) female

2 (3) 2 (3)

+ 3 (2) 3 (2) +
Com 7 (5) 7 (5) Com
RS422: furnace to furnace
female 25-pin 25-pin female
Rx+ 3 3 Rx+
Rx

16 16 Rx

Com 7 7 Com
Tx+ 12 12 Tx+
Tx

13 13 Tx

If a boxed KD485 RS485/422 to RS232 converter is supplied, then the connection cable from
furnace to KD485 should be a “straight” cable, the same as the furnace-to-furnace cable. The
connection between the KD485 and the PC should be a “crossover” cable, the same as the Furnace
to PC cable. Note that the internal wiring of the KD485 box for the 5-wire (RS422) system
includes a cross-over.