Stanford Research Systems DS360 Operating Manual And Programming Reference page 125

Front Panel Control
The front panel display board consists of eight 7 segment displays and 50 discrete LEDs.
They are arranged into eight groups, each driven by a strobe line. U501 and U502 are the
latch and drivers for the strobes. U503 and N501 are pull down latches and current
limiting resistors for the seven segment displays. U505, U506, N504, R502 and R503 are
latches, pull down transistors and current limiting resistors for the discrete LED's. U507
is the keypad input. U508 and U509 decode the direction that the knob is turning and
generate the knob interrupt to the main processor. U504 (74HC4538) acts as a watchdog
timer, shutting off the LEDs if the processor stops working.
GPIB & RS232
The GPIB (IEEE-488) interface is provided by U601, a NAT9914 controller. U602
(75160A) and U603 (75161A) buffer the data and control lines to the GPIB connector.
U601 is programmed to provide an interrupt to the processor whenever there is bus
activity addressed to the unit.
The 8251 UART (U604) provides all the UART functions, except the baud rate
(generated by U405). U605 (MAX202) provides level shifting and buffering for
incoming and outgoing data. U604 generates an interrupt whenever there is activity over
the RS232 interface.
The RS232 port is a DCE and may be connected to a PC using a standard serial cable (not
a "null modem" cable).
Power Supply
CAUTION
Dangerous voltages are present on the printed circuit board when the instrument is
attached to the power source, even if the unit is turned off! Always wait at least one
minute after removing the power before opening the unit.
The power entry module provides a connection to the power source, fuses the line, selects
the line voltage and filters out high frequencies noise. SW701 switches the line and
neutral. Transformer T701 provides all low voltage power to both the digital and analog
boards.
D701 and D702 rectify the low AC voltage for the digital section. U701 (LM7805) is a
three terminal regulator that provides +5 V
(LM7805) provides +5 V
for the cooling fan.
for most of the digital circuitry. U702
DC
for the LEDs and displays. U703 (LM317L) provides +7 V
DC
DS360 Ultra Low Distortion Function Generator
Circuit Description 7-5
DC