IBM 1 Series - Integrated Digital I;O Electrical Characteristics; Digital Input (DI) Characteristics; Digital and External Sync Input Specifications

Diagnostic Mode
The diagnostic mode is entered by performing either a Set Test Ones
command or a Set Test Zeros command. When the appropriate command
is executed: (1) the user’s inputs are disabled, (2) either 1’s or 0’s are
placed on the input receivers, and (3) the ‘external sync’ receiver is pulsed.
When subsequent Read commands are issued, the DI group responds
exactly as if the actual user inputs had been set, including the PI and
external sync functions.
Integrated Digital I/O Electrical Characteristics
Digital Input (DI) Characteristics
Each digital input (or process interrupt) point is nonisolated and is
designed to operate with TTL-compatible voltage levels. Voltage inputs up
to +24 volts may be used with this feature. Figure 5-4 shows a
representative input point. For voltages above +5 volts, the input
impedance is a function of the input voltage. Each DI point has an internal
pull-up resistor, and unconnected inputs are held at the inactive state (up
level).
+5 V
20 kQ
2kQ
User’s
input
400 pf
Common @
Figure 5-4. DI equivalent circuit
Digital and ‘External Sync’ Input Specifications
Each DI point and the ‘external sync’ input meet the following
specifications:
Input impedance: >9.2 kilohms at less than +4.5 V;
>2 kilohms at +24 V;
>2 kilohms at —24 V
Input limits: +24 Vdc, maximum;
—24 Vdc, minimum
Logical 1: <1.0 volt
Logical 0: >2.5 volts
Integrated Digital Input/Output Feature 5-7