{"id":766,"date":"2016-07-19T23:01:48","date_gmt":"2016-07-19T23:01:48","guid":{"rendered":"http:\/\/avitech.com.au\/?page_id=766"},"modified":"2025-10-18T22:38:47","modified_gmt":"2025-10-18T22:38:47","slug":"rs232-connectors","status":"publish","type":"page","link":"https:\/\/avitech.com.au\/?page_id=766","title":{"rendered":"RS232 Connectors"},"content":{"rendered":"\n\n
\n

This page sets out some basic information about serial connectors used for RS232-level asynchronous serial communications.<\/p>\n

Protocol and signal levels<\/h4>\n

When TXD and RXD lines are in the IDLE state (and for a Logic 1 on these lines):<\/p>\n

\n

TTL logic lines are at +5V<\/p>\n

RS232 lines are at -VE voltages<\/p>\n

Current is flowing in current loops<\/p>\n<\/div>\n

Here are two diagrams showing TTL and RS232 voltage levels:<\/p>\n

\n

4.bp.blogspot.com<\/a><\/p>\n

www.sparkfun.com<\/a><\/p>\n<\/div>\n

Pinouts: DB25 and DE9<\/h4>\n

\"\"<\/a><\/p>\n

DE9 and DB25 connectors usually have the pin numbers embossed on them in tiny lettering. Often it is very difficult to read however.<\/p>\n

The diagram on the right shows the pin number of DE9 connectors. Click on the image for a better view of it.<\/p>\n

DB25 connectors follow the same numbering convention, and have their Pin 1 in the same position.<\/p>\n

The full description of the DB25 pinouts (including rarely used signals) is shown in the table about one-quarter of the way down this page -> RS232 on DB25 Pinout (RS-232C)<\/a><\/p>\n

The table below shows the serial port pinout on some devices I have needed to make cables for.<\/p>\n

This image shows the pinouts of the DB25 connector from a DTE’s perspective -> V.24\/RS-232 Interface<\/a><\/p>\n\n\n\n\n\n\n\n
Computer \/ Device<\/th>\nConnector<\/th>\nTXD<\/th>\nRXD<\/th>\nDTR<\/th>\nDSR<\/th>\nDCD<\/th>\nRTS<\/th>\nCTS<\/th>\nGND<\/th>\nNotes<\/th>\n<\/tr>\n
IBM PC 25-Pin<\/td>\nDB25 M<\/td>\n2<\/td>\n3<\/td>\n20<\/td>\n6<\/td>\n8<\/td>\n4<\/td>\n5<\/td>\n7<\/td>\nPin 22 = Ring Indicator input.<\/td>\n<\/tr>\n
IBM PC 9-Pin<\/td>\nDB9 M<\/td>\n3<\/td>\n2<\/td>\n4<\/td>\n6<\/td>\n1<\/td>\n7<\/td>\n8<\/td>\n5<\/td>\nPin 9 = Ring Indicator input.<\/td>\n<\/tr>\n
VT320<\/td>\nDB25 M<\/td>\n2<\/td>\n3<\/td>\n20<\/td>\n6<\/td>\n8<\/td>\n4<\/td>\n5<\/td>\n7<\/td>\n <\/td>\n<\/tr>\n
Cromemco CS-1<\/td>\nDB25 F<\/td>\n3<\/td>\n2<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n7<\/td>\n <\/td>\n<\/tr>\n
Ferguson Big Board I<\/td>\nDB25 F<\/td>\n3<\/td>\n2<\/td>\n8<\/td>\n6<\/td>\n20<\/td>\n5<\/td>\n4<\/td>\n7<\/td>\nSee Note 1 below.<\/td>\n<\/tr>\n<\/table>\n

Note 1 (Ferguson Big Board I):<\/p>\n