Control Data Corporation INFORMATION SYSTEMS TERMINAL II Hardware Maintenance Manual page 95

The program is:
LD A, (8409H)
OR A, 20H
LD (8409), A
AND
A, ODFH
LD (8409), A
Load A register with 8-bit word
from location 8409H
OR data in A register with write
mask. This sets bit 5 of the data
without modifying the other 7 bits.
Store contents of A register in
location 8409H. The desired dot
on the screen is now illuminated.
The data just stored in memory and
still in the A register is ANDed
with the erase mask. Bit 5 is
reset without modifying the other
7 bits.
Store the A register in location
8409H. The desired dot on the
screen is now dark.
I/O Peripheral Devices - All the peripheral devices except
the display are controlled by the processor by means of I/O
instructions. These instructions perform functions, such
as transfer data, control parameters, and status informa-
tion. The secondary byte of the I/O instruction defines
the device/function with which the processor exchanges
data. Table 4-5 is a complete list of all the defined
device/functions of the terminal.
Read Configuration Switches (Input 00) - This command reads
the setting of eight switches, five of them external, the
rest on the controller board.
Load Maintenance Register (Output 00) - This instruction
transfers the data output by the processor into an 8-bit
holding register. Each bit of this register has a func-
tion, as follows:
• Data Bit 0, ERR LED - This maintenance register out-
put drives an LED labeled ERR (error). Loading a 0
in the register turns the light on (1 equals off).
This output is a 0 upon power on or reset.
82100083 4-33