HP 3562A Service Manual page 308

C I RC U I T D E S C R I PT I O N S
I n addition to read ing the front panel keys the system processor can also sou nd the beeper
when an error occu rs. To sound the beeper, the A2 System CPU sends the beeper i nstruction
to the keyboard . The keyboard processor sets the decoder output l i nes to activate the
beeper.
Rotational Pulse Generators
T h e RPGs mu st be activated before they can be used. The s ignal l i nes XL and YL activate
the marker RPG (RPG1 ) and the X and Y f ront panel L E Ds. The ENABLED signal l i ne activates
the parameter RPG (RPG 2). Si nce both RPG s ope rate in the same man ner, only RPG1 is
d escribed.
After the A2 System Processor i n stru cts the keyboard to tu rn on the X or Y L E D, the i np u t
l i nes XL and Y L activate t h e marker RPG; the output o f the t u r n latch (RPG1 ) is s e t to
a l ogic 1 . W hen the R PG is tu rned, the c l ock of the turn latch togg les between TTL level
h igh and TT L level. low. The output of the turn latch (RPG1 ) toggles the clock of the d irection
latch. The output of the d i rection latch (D I R1 ) depends on the d i rection the RPG is turned.
Afte r the RPG1 and DI R1 s ignals are sent to the keyboard processor the fo l l owing o c c u rs:
1 . The keyboard processor po l l s the R PG1 and D I R1 l i nes and I RQT2L is sent to the A2
System C P U .
2 . The system processor i n stru cts the keyboard to send its status. The status wo rd te l l s
the system processor which RPG was moved and i n what d i rection.
3 . The keyboard p rocessor asserts the C l ear RPG (C LRPG L) l i ne, clearing the turn and
i nterru pt l atches.
The system processor uses the information from the keyboard in the d ispl ay routi nes. These
routines i n c rement the marker one location i n the d irection as i ndicated by D I R1 and D I R2 .
A s the RPG m oves, the above steps are repeated u ntil n o fu rther movement o f the R P G
i s detected.
The outputs of the RPG appears as fo l lows:
T P1
C o u n terclockwise:
T P1
W hen the RPG latches are enab led, t u r n i ng of the RPG causes the RPG1 l i ne to go h i g h .
T h is c locks the d i rection latch.
6-90
MO D E L 3562A
.