Addressing The Al Board - HP 35601A Operating And Service Manual

Model 35601A
Service
After start-up, RFD is normally set high ('NRFD' = 1) and DAC is set low ('NDAC =0);
this is state 10 in Figure 6-26. When the HP-IB talker sees this, it will put data on lines
' D i o r through 'DI08\ wait for the lines to settle, then set DAV high (the HP-IB line
'DAV = 0). When the handshake circuitry sees DAV = 1, it will go to state 00, set RFD low,
and trigger MONOl. After 0.5G sec, MONOl will trigger MON02. If DAV is still high, the
circuitry will go to state 01; it will keep RFD low and set Q2 high. MON02 will generate the
latch pulse to either U17 or one of the control latches depending on the state of DI08. At the
end of MON02, the data has been latched, so 'NDAC is set high. When the listener sees
this, it makes 'DAV'(the HP-IB line) high; DAV (U29 pin 8) goes low. When the circuitry
sees DAV go low, it returns to state 10 via state 00. At this point, the handshake is ready for
another cycle.
NOTE
The latch pulse is only allowed when DAV is true and ATN is
false, as determined by U22B and U22A. At start-up, the board
will go to state 01 if DA V is true. This case should never exist, but
is defined to avoid any system hang-up.
6 81. Addressing the A1 Board.
Addressing to listen occurs when the talker sets the Listen Flip-Flop. First, the talker sets
'ATN' true (low) and 'DI01' through 'DI05' to the address of the -hp- 35601 A. 'DI06' is
set true, and 'DI07' is set false; this is HP-IB convention. The Al Board compares the data
on the ' D i o r through 'DI05' to the address of the -hp- address. This is accomplished with
U23 and U31 which also checks that '0106' is true. U29A checks that '0107' is false. If a
true comparison exists, U31 pin 6 gets high, (far out) When an address comparison exists,
and DAV is set true with ATN true, as determined by U29B, the address flip-flop (FF3) will
be set by a pulse from MON02 to U29A pin 2.
The Al board can be unaddressed in three ways:
1. At start-up with a reset pulse.
2. By 'IFC being set true by the talker.
3. When the unlisten command is sent. This is detected by U30.
When the board has been addressed to listen, LED CRl is turned on by U21E and the front
panel ADDRESSED indicator is turned on by U21F. If SWl is set to REMOTE and the
board is unaddressed, the data lines to the control latches are disabled by U25D. This is done
to prevent digital noise from leaking to the rest of the instrument because of poor isolation
from the control latches. The control latches have a different power supply for the same
reason.
6-73