NorthStar HORIZON Manual page 70

MOTHERBOARD CONTROL BYTE
A number of control functions can be executed on the motherboard
under program control. To cause a control function from a
program, a control byte code should be loaded into the A-register
and then an OUT 6 intruction should be executed. The following
table gives the control byte codes and their functions.
Code(hex)
00
10
11
12
13
14
15
16
17
18
19
lA
lB
lC
lD
IE
IF
20
30
40
50
C0
Function
Reset USARTs' arming bits, and Cf inhibit bits
Disarm parallel input interrupt
Arm parallel input interrupt
Disarm parallel output interrupt
Arm parallel output interrupt
Disarm standard transmitter ready interrupt
Arm standard transmitter ready interrupt
Disarm standard transmitter empty interrupt
Arm standard transmitter empty interrupt
Allow standard Cf bit (carrier detect)
Inhibit standard CF bit
Allow second Cf bit
Inhibit second CF bit
Disarm second transmitter ready interrupt
Arm second transmitter ready interrupt
Disarm second transmitter empty interrupt
Arm second transmitter empty interrupt
Reset parallel output flag
Reset parallel input flag
Disarm clock interrupt
Reset clock flag
Arm clock interrupt
MOTHERBOARD STATUS BYTE
The status of various motherboard conditions can be read under
program control by inputting the motherboard status byte. If a
program executes an IN 6 instruction, then the status byte is
loaded into the A-register. The following table shows the
meaning of the bits in the status byte. Note that three of the
bits can be jumpered by the user to provide special status
conditions.
Bit
o
1
2
3
4
5
6
7
Status Condition
Parallel output flag
Parallel input flag
Clock flag
User defined (J3)
Second CF bit/
Standard CF bit!
User defined (J2)
User defined (Jl)
North Star HORIZON Computer
70