I have an RS232 device that I want to connect to a CoBox Micro or CoBox Mini. How can I interface these device's TTL serial ports to an RS232 device?

Here's an ASCII diagram of an example circuit for the CoBox Micro. This example uses a single Maxim MAX232 chip to drive the RX, TX, CTS & RTS signals.

CoBox Micro                                             RS232 
Con1

SGD       2---------------------------------SGD

                           Maxim
                         MAX232
                         +-------+
RXA(IN)   3------------12|--o<---|13--------TX(OUT)
                         |  R1   |
                         |       |
TXA(OUT)  4------------11|--->o--|14--------RX(IN)
                         |  T1   |
                         |       |
RTSA(OUT) 5------------10|--->o--|7--------CTS(IN)
                         |  T2   |
DTRA(OUT) 6--NC          |       |
CTSA(IN)  7-------------9|--o<---|8--------RTS(OUT)
                         |  R2   |
DCDA(IN)  8--NC          |       |           +5Vdc
                   +----4|C2+ Vcc|16----+------O 
                   |     |       |      |
             0.1uF =     |       |      = 0.1uF
                   |     |       |      |
                   +----5|C2-  V+|2-----+
                         |       |
                   +----1|C1+  V-|6----||---GND
                   |     |       |    0.1uF
             0.1uF =     |       |
                   |     |       |
                   +----3|C1- GND|15--------GND
                         +-------+

If you need the DTR and DCD signals instead of RTS and CTS you can connect them instead. If you need all 4 handshaking signals you can either use 2 MAX 232 chips or another chip with more drivers.

Maxim has several chips in it's MAX232 line with varying numbers of drivers. Maxim's web site is https://www.maximintegrated.com/en.html.

In the US you can get Maxim parts from:

• DigiKey, http://www.digikey.com/DigiKeySearch.html
• Newark Electronics, http://www.newark.com/
• Mouser Electronics, http://www.mouser.com/
• Jameco Electronics, http://www.jameco.com/
• or you favorite electronic parts vendor.

Other possibilities are:

• National Semiconductors DS14C232
• Harris HIN232 and ICL232
• Motorola ADM232
• Linear Technology LT1137A
• • The LT1137A is a little different from the MAX232.  It has 3 RS-232 outputs and 5 inputs.

[Originally Published On: 01/26/2000 08:39 AM]