HP 3562A Service Manual page 307

MOD E L 3562A
6-1 1 A 1 5 KEYBOARD
Refer to f i g u re 6-A1 5 for th i s d iscussion. -The keyboard provides operator i n p u ts to the
H P 3562A as wel l as operation feed back i n the form of status L E Ds . The three major
fu ncti ons of this assembly are:
1 .
To send the code of any key pressed to the A2 System C P U .
2 . To i n d icate operatio n a l status with L E Ds.
3. To inform the A2 System C P U when the rotational pulse generators (RPG1 , RPG2) have
been enabled .
LED IndIcators
The A2 System C P U sets the appropriate system d ata l ine (DOL to D7L) for the L E D which
i s to be tu rned on. Next, the system processor asserts the instruction l i nes for the keyboard
(A1 L, A2 L, W R IT E L, K Y B R D L). After these l i nes are set up, the add ress strobe (AS L) l ine
is asserted w h i c h causes the keyboard p rocessor to be i nterru pted by the keyboard select
(KYS E L) s i g n a l . When i nte rru pted, the keyboard p rocessor reads the i n stru ction l i nes and
causes L E D1 L or L E D2 L to latch the system d ata to the L E Ds.
Front Panel Key Pressed
The keyboard processor contin u ou s l y i n c rements its output port except when it is i nter­
fac ing with the system C P U . The output port controls a BC D-to-dec i m a l decoder and
mu ltip lexer. When a key is p ressed by the operator, an i n pu t l i ne to the m u ltip lexer is
grounded and the K E Y l i ne is asserted. When the keyboard p rocessor senses the asserted
K E Y l ine, it reads the m atrix cou nter, and stores the value i nterna l ly. At the same time,
the keyboard processor asserts I RQ cau s i n g the i nterrupt req uest ( I RQT2 L) s ignal to be
sent to the system p rocessor.
The system p rocessor a lways responds to a keyboard i nte rru pt req uest by f i rst send ing
a status request i nstruction to the keyboard. This instruction causes the follow i ng to happen:
1 . The output regi ster enab led (O R E G E N L) signal i s asserted.
3. The status is stored in the data output register when O R E G L i s asserted .
4.
The C L RPG L l i ne is asserted to c l ear the I RQT2 L l i ne.
5. The DTAC K L signal is sent to the A2 System CPU to i n d i cate the d ata was transferred�
6.
The A2 System C P U reads the status word to determ i n e what has occu rred on the
keyboard .
7. The A2 System CPU sends an instru ction to the keyboard processor to output the val u e
stored i n the keyboard m atrix cou nter. T h i s va l u e is the key code.
8. The Key Code is read by the system p rocessor to determ ine what key has been p ressed .
C I RC U I T D E SC R I PT I O N S
6-89