HP 3457A Service Manual page 184

© Sets the read/write (R/W) output (USO1 pin 32) high.
© Sets address line AI5 high to enable gate U598b.
The combination of the positive portion of timing signal €+a and the high R/W signal causes a negative
pulse at the output of gate U598d (RD). Simultaneously, the positive portion of timing signal E+9 and the
high A1I5 signal cause a negative pulse at the output of US98b (ROM).
The negative ROM signal activates the output of ROM
US02 and causes a negative pulse at the output of
gate U596b to enable tri-state buffer U517.
The negative 80 signal from U598b activates the output of
buffer U5SI7. The
microprocessor
then reads the information
from primary
data
bus "A", lines DO
through D7.
8-43. Reading information from RAM U506.
To read information from RAM U506, the microprocessor:
© Sets the read/write (k/W) output (U501, pin 32) high.
© Sets address lines Al4 high and AI5 low to enable decoder US13.
The low portion of timing signal &
(U597b, pin 4) activates the RAM output of decoder U513 to enable
RAM U506.
The positive portion of timing signal €+a and the high k/W signal pulses the output of gate
U598d (RD) low to activate the output of RAM
US06.
The microprocessor then reads the information
from data bus "A", lines DO through D7.
8-44. Reading information from RAM U511.
To read information from RAM USII, the microprocessor:
© Sets the read/write (R/W) output (U501, pin 32) high.
HP 3457A Multimeter
8-19