Virtual Console - Data General NOVA 4/S Manual

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maintenance of DGC equipment and software. The drawings and specifications contained herein are the property of DGC and shall neither be reproduced in whole or
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VIRTUAL CONSOLE
The virtual console (VC) allows you to interact with the
computer through the system terminal connected to the
CPU's on-board asynchronous communications interface.
Simple commands which you enter on the terminal
keyboard allow you to examine and/or modify
processor registers or memory locations, start, stop, and
continue program execution, and initiate a program load
from a selected device.
On power up, the computer performs a self-test. After a
successful completion of the self-test, the following
information is typed on the terminal:
OK
1000000
'
"OK" followed by "!' indicates that the self-test ran
successfully. This, in turn, is followed by the contents
of the program counter, which is all zeroes on
power-up. The next "!" is the VC prompt; it tells you
that VC is ready and at your service.
In addition to power-up, VC is entered when:
e A HALT instruction is executed,
e The RESET switch on the front console is pressed
and the front console is unlocked; or
e The Break key on the system terminal is pressed
and the front console is unlocked.
Under these conditions, the contents of the program
counter when VC was entered is typed. This is followed
by the '"!' VC prompt. For example, if the program
counter was at location 2077 when VC was entered, the
following would be typed:
002077
'
12
VC operates on cells. A cell is either a memory
location (memory cell) or an internal register (internal
cell) such as an accumulator. Each internal register that
is accessible by VC is assigned an internal cell number.
These are listed in Table 2.1.
Table 2.1
INTERNAL CELLS
internal Internal Register
0-3 The contents of the accumulators ACO through AC3
respectively.
4 Return address (the contents of the program counter
when VC was entered).
5 Stack pointer
Frame pointer
Interrupt enable flag status bit:
O = interrupts off
1 = interrupts on
10 MMPU status bits before VC was entered (NOVA 4/X
only):
BIT MEANING WHEN 1
O Program mapping enabled
1 Data channel mapping enabled
2 Program map inhibited
3-8 Reserved for future use
9 Single cycle write protect enable
10 Single cycle select (0 = A, 1 = B)
11 Auto increment/decrement protect
12 Defer protect enable
13 1/O protect enable
14 Write protect enable
15 Program map select (0 = A, 1 = B)
11 Data switch register:
Replaces the conventional console data switches. When
the system is in run mode (i.e., not in VC mode) and a
READS instruction is executed, the 16-bit contents of
this register are read by the CPU.
12 Value of the carry bit
In order to examine or modify any cell, you must open
it. Opening a cell causes its contents to be printed, in
octal, on the terminal.