Wang 5536 - Page 28

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2.3.2.2 Data Link (Figure 2-8)
The data link permits the Master to transfer data at high speed between its
main memory (or disk) and main memory in its peripheral subsys terns. The ,
data link residing in 5536 workstations permits high speed, bidirectional
data flow between the Master Unit of each system and its 5536 work-
stations. In particular, the Master uses this link to load programs into
workstations, store documents produced at workstations, and to feed
high-speed printers.
Each workstation is connected to the Master separately, through a radial
bus structure. All transmissions are controlled by the Master.
Data is transferred directly between memories using DMA logic. Data
transfer is carried out in a serial, asynchronous, byte-oriented format
using a half-duplex line. The transmission line itself is a balanced pair
of coaxial cables operating at 4M baud. The actual data transfer rate is
approximately 260K bytes per second.
o Data Link Commands
Six Data Link commands permit the Jitaster to:
- Check Slave STATUS and ID
- Initiate Slave Operatio;-(RESTART)
- Load Slave Memory (WRITE -- 2 commands)
- Store Slave Data (READ -- 2 commands)
STATUS and ID commands send Slave STATUS and ID to the Master on command.
RESTART conunands reset the Slave CPU on command from the Master.
WRITE and READ commands may each transfer either 1 byte or 256 bytes.
One-byte commands transfer a single DMA cycle.
Two-hundred-and-fifty-six-byte commands transfer a single page of data.
Write Data (1 byte) commands the Slave to receive data (one DMA cycle)
from the Master on command.
Write Byte (256 bytes) commands the Slave to receive data (one page)
from the Master on command.
Read Data (1 byte) commands the Slave to send data (one DMA cycle) to
the Master on command.
Read Byte ( 256 bytes) commands the Slave to send data (one page) to the
Master on command •.
The Data Link contains four logic functions:
Data Path
Timing
Line Control
Command Decode
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