User's Manual

TS4000 Radio Modem User’s Manual Appendix A - Serial Ports 81
Serial port 1 can be configured for either RS-232 or TTL signal levels. The signal
level selection is controlled with internal jumper plugs (see Appendix F - Internal
Jumper Block).
Signal Levels
The RS-232 standard defines minimum and maximum voltage levels for the
drivers and receivers. However, in practice the drivers and receivers work
correctly with signal levels that are different from the specification.
RS-232 Signal Levels
Level (volts DC)
Type Low High
Drivers (into a 3k to 7k ohm load)
RS-232 Specification
Actual TS4000 Drive Levels
-15 to -5
-9 to -6
+5 to +15
+6 to +9
Receivers (with 3k to 7k ohm load)
RS-232 Specification
Actual TS4000 Receive Levels
-25 to -3
-25 to +0.8
+3 to +25
+2.4 to +25
Level (volts DC)
Type Low High
Output (Driver) 0.0 to +0.4
(sinking up to 4 mA)
+3.0 to +5.0
(sourcing up to 4 mA)
Input (Receiver) -25 to +0.8 +2.4 to +25
(3k to 7k ohm load)
TTL Signal Levels
The signal polarity is the same for both RS-232 and TTL operation.
Signal Polarity
Level State
Voltage Low Mark
Control signal inactive
Stop bit state (end of async character)
Logic one data bit state (within async character)
Voltage High Space
Control signal active
Start bit state (beginning of async character)
Logic zero data bit state (within async character)