TM 11-5895-856-34-1/EE640-CA-MMI-010/ E154 CPU/TO 31W2-2T-122-1
I/O channels. The primary function of the PPI is to
directly from memory. Normal transfer of data to or
from the disc is accomplished with the RASC in the
transfer single blocks of data from the online or
transmitting CPU to the off-line or receiving CPU.
direct memory access mode. All data read from the
disc is checked for correct parity. Data written into the
Either CPU can initiate the action. In any single block
32,768 words may be transferred with a transmittal rate
memory has correct parity added by the RASC.
of up to 50,000 words per second. The data is
transmitted in the word mode only.
Functional
2-22. Processor-to-Processor Interface
organization of the PPI is shown in the block diagram
The processor-to-processor interface (PPI) is a unit
which interfaces the two processors through standard
Figure2-6. PPI Functional Block Diagram
The CPU that is sending data will initiate the sequence
thus preventing the possibility of both CPUs being on-
by executing an input-to-register (ITR) to determine the
line at the same time. The on-line CPU will issue one of
PPI status. If neither CPU is on-line, the interrogating
the following two device commands: Start 1-initiate
CPU is made on-line, and the status byte is
priority information transfer; i.e., starting address, block
automatically modified. If simultaneous interrogations
length, special status, etc.; and Start
are executed by both CPUs, one will be given priority,
2-11
Previous Page
