ksbszabo@wateng.UUCP (Kevin Szabo) (09/15/84)
A friend of mine asked for some information about RS 232 and I decided to type this table in. Being a generous sort, I figured the rest of you might like it. If you find any errors please update the table and repost. I'm leaving the country for a couple of months and so won't be able to respond to any mail replies. Kevin Szabo Feed through tbl, and then troff with the -ms macros. ---------------------------------------------------------------------- .nr PO 0.5i .nr LL 7.0i .LP .SH RS-232 Signal Conventions .LP The signal threshold is +- 3 volts, with preferred signal levels around +-12 volts. Military usage specifies +-24 volts. For data: `1'=Negative Signal, `0'=Positive Signal. For control signals: ON is positive, OFF is negative. .LP DTE stands for Data Terminal Equipment, DCE stands for Data Communication Equipment. .LP The signal flow is: Computer <-> DTE <-phoneline-> DCE <-> Terminal. .LP I am not really sure how the signal CI/CH works, the data signal rate selector. I believe all the timing signals provide a clock, as opposed to a code representing the transmission speed. .LP .TS center, box; n | c s | c s | c s | c | l n | c c | c c | c c | c | l. Pin Data Control Timing Circuit Description DCE DTE DCE DTE DCE DTE _ 1 AA Protective GND _ 2 \(bu BA Transmitted Data _ 3 \(bu BB Received Data _ 4 \(bu CA Request to Send _ 5 \(bu CB Clear to Send _ 6 \(bu CC Data Set Ready _ 7 AB Signal Ground _ 8 \(bu CF Received Line Sinal Detector _ 9 - Reserved for Data Set Testing _ 10 - Reserved for Data Set Testing _ 11 - Unassigned _ 12 \(bu SCF Secondary Signal Detector _ 13 \(bu SCB Secondary Clear To Send _ 14 \(bu SBA Secondary Transmitted Data _ 15 \(bu DB Transmission Signal Element Timing _ 16 \(bu SBB Secondary Received Data _ 17 \(bu DD Receiver Signal Element Timing _ 18 - Unassigned _ 19 \(bu SCA Secondary Request To Send _ 20 \(bu CD Data Terminal Ready _ 21 \(bu CG Signal Quality Detector _ 22 \(bu CE Ring Indicator _ 23 \(bu \(bu CI/CH Data Signal Rate Selector _ 24 \(bu DA Transmit Signal Element Timing _ 25 - Unassigned .TE .LP The Data, Control and Timing Columns denote the Signal source, i.e. Data Set Ready is asserted by the DCE. .LP .SH How To Make A Null Modem .LP Generally this connection scheme works, but be careful since some manufacturers have applied their own meaning to the signals Request to Send and Clear To send, especially when the terminal tries to do BOTH soft and hard flow control. Some do this by dropping request to send when they are practicing hard flow control. The loopback scheme shown here will prevent the terminal from resending XON to restart soft flow control, thus locking up the terminal. If you have a terminal which only does one type of control at a time this connection should work. .LP The source of this information is from DEC's handbook for PDP-11, that describes the H312, and asynchronous null modem. .LP For connectors A and B, connect the following signals together: 1A to 1B (protective ground). 2A to 3B (data), 3A to 2B (data). 4A to 5A to 8B (loop back the Request To Send to Clear To Send and to Carrier Detect). 4B to 5B to 8A (same again). 20A to 22B to 6B (Data Terminal Ready to Ring Indicator to Data Set Ready) 20B to 22A to 6A (same again). .LP -- Kevin Szabo watmath!wateng!ksbszabo (U of Waterloo VLSI Group, Waterloo Ont.)