Control Data Cyber 170 State Hardware Reference Manual page 57

InputlOutput Unit
PP
Memory
Each PP has an independent
4K
or 8K word memory. Each word contains 16 data
bits, with the upper 4 bits set to 0, and 6 SECDED bits. PPO
executes the
deadstart program from the microprocessor
RAM
during the deadstart operation.
PP memory 0, therefore, must be operational. A PP memory reconfiguration
feature allows the user to restore IOU operation if the IOU detects a fault in
the PP memory normally assigned to PPO.
To reconfigure, the operator assigns a good PP memory to PPO and the operating
system removes the failing PP memory. Computer operation can continue without
the failing PP memory, and repairs can be made during scheduled maintenance.
The system must be deadstarted to reconfigure PPMs.
I/O Channels
The I/O channels are composed of:
0
An internal interface that allows common hardware and software to control
the external devices, and
0
An external interface that allows the IOU to communicate with the external
devices using 12-bit data channels. The internal interface can transfer
16-bit data words between two PPs or between a PP and an external device at
a maximum rate of
1
word every
250
ns.
This rate can be sustained for the maximum practical channel transfer (4096
words). During transfers between PPs, if the PPs are in the slot at the same
time, the transfer rate is 500 ns.
Any PP can access any of the CYBER 170 bidirectional 110 channels. All PPs
communicate with external devices through the independent 1/0 channels.
Each
channel may be connected to one or more pieces of external equipment, but only
one piece of equipment can use a channel at one time. All channels can be
active simultaneously. Available channels are:
Twenty-four CYBER
170
compatible I/O channels available with a maximum data
transfer rate of 3 ~bytes/second.
An optional, DMA-enhanced, intelligent standard interface (ISI) channel
adapter, intelligent peripheral interface (IPI) channel adapter or CYBER
1
170 channel adapter that can be installed in any one of ten channel
locations in the CIO cabinet. The adapters transfer data between the IS1
or CYBER 170 channel and PP memory using standard I/O instructions. They
also support
DMA
transfer in which data goes directly between CM and an
external device without going through the PP. There are two types of CYBER
170 DMA
transfers, fast and normal. Fast transfers are used with the
Extended Semiconductor Memory-11 (ESM-II), and normal transfers are used
with other CYBER 170 external devices.