IBM 1 Series Manual page 132

Outputs
Current Driver (No Customer Supply Required). The teletypewriter adapter
card provides a current driver for transmit output. The current driver
provides the current to drive the transmit loop. No external power supply
is required if this current driver output is used to drive the OEM device
receive input.
Whenthe current driver is '"'on,'' a maximum current of 20 mA out of the
teletypewriter adapter card is generated. The voltage across the transmit
output pins when the current driver is on is:
Vi. = I to R, where the exact current flowing is
I,= LV
620+R
R is the impedance looking into the OEM device receive input pins. For
reliable operation, R should be less than 200 ohms.
Whenthecircuit driver is off, the maximum current out of the transmit
output is 500 vA and the voltage across the transmit output pins is V,, =
0.0005 R.
Solid-State Switch (With Series Customer Supply). The teletypewriter
adapter transmit output is a solid-state switch. In the open or off-state, the
maximum voltage the switch can withstand is 52.8 volts. With this voltage,
the maximum current through the switch is 500 uA orless.
In the closed or on-state, the maximum permissible current through the
switch is 100 mA. The voltage drop across the switch in the closed or
on-state must be less than 0.08 volt.
Solid-State Switch/TTL (Without Series Customer Supply). In the open or
off-state, the maximum output voltage is 5.5 volts at 50 nA; the minimum
output voltage is 2.4 volts at 1 mA.
In the closed or on-state, the maximum output voltage is 0.8 volt; the
minimum output voltage is 0.0 volt.
EIA. The EIA outputs must conform to EIA RS232-C/CCITT V.24
specifications. The output driver is an SN74150 TTL driver.
If the +12-volt supply is not installed, the 'EIA transmitted data' signal
and the 'EIA data terminal ready' signal are in the power-off condition.
For attached devices using the EIA input for receive-only operations, the
+12-volt supply option is not required. In this case, the 'EIA data terminal
ready' signal generated by the attached device should be wrapped back to
the input that would normally be connected to the 'data terminal ready'
output of the teletypewriter adapter.
Teletypewriter Adapter Feature 4-27