Multiplexed Microprocessor Bus Timing - Wavetek 75 Instruction Manual

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Figure
4-7.
Multiplexed Microprocessor Bus Timing
memory and waveform memory sections to generate
control lines. The 2 input "and" gate, U6D, is used to
produce a buffered version of the "E" clock due to the
limiteddrive capabilitiesof the microprocessor. The line
drivers in U37 and the "exclusive or" gates in U34 are
used as buffers and are transparent to the micro-
processor and external circuitry. They provide improved
drive characteristics for some of the microprocessor
outputs.
Besides the address and data buses the microprocessor
also has eleven pins configured as data outputsand one
pin configured as a data input. U30 pin 13 (SERD) out-
puts the data, in a serial form, that controls the phase
lock loop in the frequency synthesizer and the control
shift register (ref: schematic 01 03-00-1 456 sheet 2). U30
pin 14 (SERC) is used as a clock to input the serial data
into theshift registers in both circuits. U30pin 15(PLLE)
and pin 16 (ANLE) are used to enable the new data to
the phase lock loop and thecontrol shift register respec-
tively. U30 pins 17, 18 and 19 (FRBIT3, FRBIT2 and
FRBITl) control the frequency range dividers in the fre-
quency synthesizer (ref:schematic 01 03-00-1 456 sheet
2). U30 pin 8 (KWl), pin 10 (KW2) and pin 20 (KM) are
used by the microprocessor to interface to the knob
interrupt circuit in the front panel interface (ref:
schematic 01 03-00-1 389 sheet 3). This circuit provides
the microprocessor with information from the control
knob on the front panel. Pin 11 of U30 (BLOAD) is used
to place a temporary load on the battery to test its con-
dition. Pin 12 of U30(BTST) is configured as an input and
is used to read the status of the battery during this test.
The interrupt input of the microprocessor is on pin 5
(IRQ). This input is held high by the resistor R15 unless
it is pulled low by a circuit requesting service. When IRQ
is pulled low the microprocessor stops its main program
flow and begins a execution of an interrupt service
routine. This routine begins by querying the various cir-
cuitsas towhat pulled the interrupt. Action is then taken
to handle the needs of the interrupt. Once those needs
have been met, main program flow resumes.
The RESET input of the microprocessor (U30 pin 6) is used
to inhibit operation while the instrument power is being
turned on or off. This prevents the microprocessor from
outputting bad data and control bits that would disturb
the instrument setup. When the instrument is first turned
on, pin 6 is held low by the power onloff reset circuit until
the power supplies and internal clock generator of the
microprocessor have stabilized. When RESET does go
high, the microprocessor automatically fetches data from
the last two locations in memory. Thisdata is the address
of the memory location the microprocessor must access
in order to begin normal execution.
Scans by Artekhledia O 2006