Control Data Cyber 170 State Hardware Reference Manual page 68

Operating Procedures
Deadstart Sequences
In response to a keyboard command (L or S) to the deadstart display, the IOU
performs a deadstart sequence. Depending on the command (L or S ) , either the
long or the short deadstart sequence is performed. The short deadstart
sequence is used when hardware integrity verification is not required. The
long deadstart sequence performs all the tasks performed by the short deadstart
sequence and some additional tasks. The main additional task is the running of
a diagnostic program, from a read-only memory (ROM) in the IOU on logical PPO.
The diagnostic program takes approximately 15 seconds to run.
Both deadstart sequences begin with a master clear, which sets up all P P s
except logical PPO, for a 4096-word block input starting at PP location
0.
The
input into each PP is from the c h a ~ e l with the same number as the logical
number of the PP concerned. The master clear also resets all external devices
and sets maintenance channel connect code bit 52. The individual registers are
set as follows:
Register Initialization Description
K
0071008 Instruction display.
Causes block input to
start from location 0 .
A
10,
O O O ~
Count of 4096 words,
Q
0, 1, 2...
I/O channel numbers
(PPO: 0, PP1: 1, and
so o n ) .
All registers in both barrels are set to these values, except the registers of
PPO
.
If the long deadstart sequence is being performed, hardware clears location
7777 in all PP memories and sets the
P
register of PPO to the value indicated
by tae parameter U S ADDR
=
xXXX
(normally 6000s). PPO starts performing a
test program from a read-only memory in IOU. Hardware errors cause the LDS
program to hang before completion.
In the absence of errors, execution
proceeds until the test program reaches location 7776
.
When this happens,
the unique part of the long deadstart sequence ends wgth a master cleat.
Next, both deadstart sequences clear PPO location 0, write the deadstart
program on the display into PPO memory locations 1 to 208, and clear PPO
location 21
.
PPO then starts executing the program entered from the
deadstart dgsplay, which is normally a bootstrap program to input more data
from an assigned external device.
The short deadstart sequence does not disturb PP memory other than PPO
locations 0
to Zlg. Both deadstart sequences leave all PPs, except PPO,
waiting for a block input or for action through the maintenance channel.
After
the block input is completed, each PP starts executing the program entered from
whatever address was entered into location 0 of that PP.