Agilent Technologies 35670A Service Manual page 376

LPFCLK
MDACCSn
PFWn
PREFS
PVALID
RA1 - RA5
RD24 - RD31
RDTACKn
RRESETn
RRW
RSI
RSO
SCL
SDA
SHUTn
SINTn
Voltages and Signals
A99 Motherboard
Low Pass Filter Clock — This is a control line from the A6 Digital assembly's digital source.
This line controls the cut-off frequency of the A5 Analog assembly's programmable low pass
filter.
Source Attenuation DAC Chip Select — This is a control line from the A6 Digital assembly's
digital source. A low on this line enables the Attenuator DAC and DC offset DAC on the
A5 Analog assembly.
Power Fail Warning — This line goes low 10 ms before the A98 Power Supply assembly's
output voltages fall out of regulation. A low on this line tells the A7 CPU assembly to prepare
for power down and opens a relay which disconnects the source output on the A5 Analog
assembly. This line goes low in response to SHUTn going low or when the supply voltage is
disconnected or is too low.
Pre-Sample Clock — This is a 262.144 kHz clock. This clock is at the same frequency as the
system sample rate, but it is inverted and advanced in time by 100 ns.
Power Valid — This line is high when the +5 V supply from the A98 Power Supply assembly
is stabilized.
Rear Bus Address Lines — These lines are a buffered form of the A7 CPU assembly's
microprocessor address bus. The CPU assembly uses these lines to address different circuits on
the A10 Rear Panel assembly.
Rear Bus Data Lines — These bidirectional data lines are an extension of the A7 CPU
assembly's digital data bus. These lines allow communication between the CPU assembly and
A10 Rear Panel assembly.
Rear Bus Data Transfer Acknowledge — A low on this line terminates asynchronous bus
cycles.
Rear Reset — A low on this line resets the digital logic on the A10 Rear Panel assembly. This
line pulses low during power-up and power-down and when the A7 CPU assembly's
microprocessor executes the RESET instruction or is externally reset.
Rear Bus Read/Write — This line is high during a read cycle and low during a write cycle.
This line is an extension of the processor read/write line (PRW).
RS-232 Input — This is the serial RS-232-C receive data line. This line transmits data to the
A7 CPU assembly from peripheral devices one byte at a time.
RS-232 Output — This is the serial RS-232-C transmit data line. This line transmits data from
the A7 CPU assembly to peripheral devices one byte at a time.
Serial Clock — This is the serial clock for the IIC bus. The IIC controller on the A7 CPU
assembly generates this clock to synchronize the transfer of data on the IIC bus.
Serial Data — This is the IIC bus bidirectional data line. This line transmits data to or from the
A7 CPU assembly in 8-bit frames. The IIC controller on the CPU assembly controls data
transfers on the IIC bus.
Power Supply Shut Down — A connection to ground on this line forces all Power Supply
output voltages to zero. This line is normally an open circuit, but becomes a connection to
ground if the analyzer's internal temperature becomes excessive or if the power supply is
operating on dc power and no measurement has been made within 30 minutes.
Serial Interrupt — This is the IIC bus interrupt line. A low on this line interrupts the A7 CPU
assembly.
9-32
Agilent 35670A