Stanford Research Systems DS345, Manual

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BOTTOM PC BOARD
POWER SUPPLIES (SHEET 1 OF 7)
All of the DS345 circuitry is referenced to an internal ground that is floating
from the chassis ground. The interface board (see sheet 5) contains the only
circuitry that is earth-ground referenced.
The +/- 15 volt unswitched power supplies are regulated by 3-terminal regu-
lators U100 and U101. The remaining supplies are referenced to a precision
5-volt reference, U108. When shut down, the regulators are still active, but
regulating to near zero volts. The following description is of the +15 volt reg-
ulator, but the other regulators function in an analogous manner. The heart
of the regulators is a three terminal regulator, in this case U103. The adjust
pin of the regulator is controlled by op-amp U109, which compares the divid-
ed output of U103 to the 5-volt reference. The op-amp is heavily compensat-
ed, so the work of regulation falls primarily on the regulator.
The logic supply for the interface board is provided by 3-terminal regulator
U107, and comes from a separate, chassis-ground referenced winding of the
power supply transformer T100.
A line-synchronous TTL signal is provided for triggering by U110A.
MICROPROCESSOR SYSTEM (SHEET 2 OF 7)
Instrument control is provided by U200, a Z8800 microprocessor with 64k
bytes of ROM and 32k bytes of RAM. The RAM is backed-up by battery
BT200 to store instrument settings. U201 is the buffered data bus transceiv-
er, and U205 generates the system port strobes. U210A is a one-shot that
enables the front-panel LEDs as long as the processor is running and writing
to port 18H. This shuts off the multiplexed front-panel LEDs and prevents
their failure if the processor should stop for any reason.
Power up/down reset is provided by the reset circuit consisting of Q201 and
Q202. On power up, reset is released only after C204 charges through R210
from the 5-volt logic supply. On power down, Q202 discharges C204 through
R211. Q202 is turned on by Q201, which uses the stored energy in C205 to
operate as the 5-volt logic supply goes away.
JP500 is the interface connector to the communication board. (see sheet 5)
DISPLAY AND KEYBOARD (SHEET 3 OF 7)
Input port U302 provides input from the strobed front panel keypad. Input
port U301 provides input for dip switch SW300, as well as misc. input bits for
HOST ACKNOWLEDGE, TRIGGER ERROR, and A/D COMPARE.
The LED strobe lines come from U306 and are buffered by Q301-Q306.
8-1
DS345 Circuit Description