Principles of Operation 91
Figure 4-6. GPIB Board, Simplified Block Diagram (Models Agilent 664xA and 665xA Only)
Terminal strip TB101 can be strapped to provide one of four digital input/output control signals (see Table 4-4). The Power
Supply Operating Manual describes how to select one of these three sets of signals. As shipped from the factory, this
terminal strip is connected for FLT output and INH input. Refer to the Operating Manual for operating instructions.
Table 4-4. TB101 Terminal Strip, Digital CNTL Signals
PIN Digital I/O Relay Link Fault/Isolation
Pin 1 OUT 0 RLY SEND FLT Output
Pin 2 OUT 1 NC FLT Common
Pin 3 IN/OUT 2 RLY RTN INH Input
Pin 4 Common Common INH Common
The bias supply (+5 V reference to earth ground) for the primary interface circuits is located on the A2 board. It also
provides the bias voltage to operate the circuits located on the front panel board, the LCD, and the keypad. A power clear
signal (PCLR) is generated to initialize certain primary interface circuits and front panel circuits when the unit is turned on.
Isolator Board Circuits for Agilent Models 654xA and 665xA Only (Figure 4-7)
The isolator board performs the following two functions:
1. Creates a +5 V bias voltage.
2. Provides isolation between the PCLR, RxD, and TxD front panel signals and similar signals received from the A1 Main
Board.
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