Other Components, Instructions And; Commands - IBM 7090 Instruction-Reference

The address of 00005 in the PC, through the AR and MAR, brings the next instruction
to the SR and PRo Decoding the PR, the CPU operation is store and the address-- SR
(21-35) --at which to store is 00011. The PC advances to 00006. Sum C in the AC, be-
cause of decoding store, goes to the SR after SR (21-35) goes to the AR and MAR. Then
storage accepts SR to the memory data register (MDR) and stores it at address 00011.
The operation is now complete and sum C is stored for printing.
The only remaining task for the C 'pU is to tell channel A to start the printer and to
give channel A the address of C. The next instruction, coming from 00006 as dictated
by the PC, decodes as write select. The PC advances to 00007. Again, as in read select,
the channel and unit selection is in the address field of the instruction. The bit configura-
tion there indicates the printer on channel A. Channel A acknowledges the selection if the
printer is ready. This frees the CPU to ask for another instruction, this time from 00007.
The instruction, decoded in the PR, directs the resetting of channel A registers and the
loading of a command from the address found in the address field of the instruction. In
this case, SR (21-35) has the address of the command. The address goes to adders 3-17,
then to the AR and MAR. Storage delivers the contents of this address, 00013, to chan-
nel A instead of the CPU because of controls set up by the PRo
By this time, the PC had advanced to 00010, so when channel A has received its com-
mand, the CPU receives the contents of 00010 as an instruction. Decoding a PR of zeros
causes the CPU to stop. The operation code of zeros is called halt and transfer. If the
CPU should be restarted, the address field of 00010, which is all zeros, would go to the
PC and the program would restart at 00000.
The role of the CPU in A+B
=
C, print C is now ended. However, channel A still
has to print C. The printer is started and channel has a disconnect command in the
operation register, a word count of one, and the address of C--00011--in the CAC.
These all came from storage location 00013 as the CPU executed the instruction at
00007. Channel sends 00011 from the CAC to the MAR. Sum C comes back to the DR,
and the WC steps to zero. As soon as the printer is ready to receive C, the word goes
from the DR to the calculator exit and is printed. Channel A is also finished now, and
A+B
=
C, print C has been accomplished.
If you have followed the program for A +B
=
C, print C, carefully, referring to
Figure 2.3-1, you should now have a general idea of the operation of the 7090 system.
2.5.00 OTHER COMPONENTS, INSTRUCTIONS, AND COMMANDS
The preceding explanation is simplified, and many components and functions are
omitted. Before continuing with a study of this manual, study the instructions and com-
mands described in IBM 7090 Data Processing System Reference Manual, Form
A22-6528.
Figure 2.5-1 shows two other possible configurations of the CPU instruction word:
Figure 2.5-2 is a more complete representation of system components. These figures
will prove helpful in studying the 7090 Reference Manual.
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