controller. Each word transfer in a data channel operation requires a request from the device to use the DCH
facility. Special data channel control and mapping logic accelerate the execution of these operations.
Data transfers over the BMC bus are set up using PIO and executed by the BMC controller. The BMC controller
allows a block of words to be transferred between a peripheral controller and system memory at higher speeds
than data channel transfers. Up to 256 words can be transferred in a burst with a single BMC request from a
device. Figure 3-8 shows the major functional elements of the input/output subsystem:
•
PIO/DCH controller
•
ECLIPSE I/O bus
•
Burst multiplexor channel controller
TO/FROM
SYSTEM
MEMORY
AND CPU
PROGRAMMED I/O
AND
DATA CHANNEL
CONTROLLER
I ECLIPSE I/O
BUS
(48 BIT)
f/
■
//00
=WNW
TO/FROM
DATA CHANNEL
AND PIO DEVICE
CONTROLLERS
FS-12753
S-BUS (32-BIT)
•
■
••••
=IMMO
=WNW
OIMININO OMNI
BURST MULTIPLEXOR
CHANNEL
CONTROLLER
BMC BUS
INPUT/OUTPUT SUBSYSTEM
(84-BIT)
••••••
■
IMMJ
TO/FROM
BMC DEVICE
CONTROLLERS
ALI
ALO
Figure 3-8. Input/Output Subsystem, Block Diagram
3.2.11.1 Programmed I/O /Data Channel (PIO/DCH) Controller - The PIO/DCH chip performs several key
functions within the I/O subsystem including control of PIO and data channel operations; implementation of basic
I/O devices; and support for the system control program (SCP).
3.2.11.2 Operational Overview - The CPU executes PIO instructions by sending a command over the S-bus to
the PIO/DCH controller and requesting a data transfer in the appropriate direction. The PIO control logic within
the PIO/DCH controller responds to the command by generating the appropriate I/O bus control signals for
performing the specified transfer.
When PIO commands are directed to devices internal to the PIO/DCH chip itself, the logic for these devices
recognizes their device code and responds accordingly. These basic I/O devices are the real-time clock (RTC),
programmable interval timer (PIT), primary asynchronous line controllers, and ECLIPSE power fail monitor. The
PIO/DCH chip also provides support for an SCP interface.
043-003621
3-20
DGC
CONFIDENTIAL - INTERNAL USE ONLY
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