Keithley 2182, Service Manual, Page: 54 / 120

Troubleshooting 4-7
Memory circuits
ROMs U102 and U103 store the firmware code for instrument operation. U103 stores the
D0-D7 bits of each data word, and U103 stores the D8-D15 bits.
RAMs U104 and U105 provide temporary operating storage. U104 stores the D0-D7 bits of
each data word, and U105 stores the D8-D15 bits.
Semi-permanent storage facilities include NVRAM U112. This IC stores such information as
instrument setup and calibration constants. Data transmission from this device is done in a serial
fashion.
RS-232 interface
Serial data transmission and reception is performed by the TXDB and RXDB lines of the
MPU. U110 provides the necessary voltage level conversion for the RS-232 interface port.
IEEE-488 interface
U106, U108 and U109 make up the IEEE-488 interface. U106, a 9914A GPIA, takes care of
routine bus overhead such as handshaking, while U108 and U109 provide the necessary
buffering and drive capabilities for the data, control, and handshake lines.
Trigger circuits
Buffering for Trigger Link input and output is performed by U113. Trigger input and output
is controlled by the IRQ4 and PB3 lines of the MPU.
At the factory, trigger output is connected to line 1 of the Trigger Link connector (resistor
R145 installed). Trigger input is connected to line 2 of the Trigger Link connector (resistor R142
installed).
Analog circuitry
Refer to Figure 4-3 for the following discussion of analog circuitry.