
Tandberg Data
Hardware Interface
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Tandberg SLR Reference Manual
8-11
8.4.6. Command Phase
The Command Phase follows directly after Selection or Identify Message Out. It allows the
Target to obtain command information from the Initiator.
The Command Phase is entered with BSY and C/D asserted and SEL, ATN and I/O
deasserted. After a bus settling delay of at least 400 ns the Target requests the first byte in
the Command Descriptor Block by asserting REQ. The Initiator responds by placing the first
byte on the bus and asserting ACK. The Target notices this and deasserts REQ. The Initiator
should then deassert ACK.
The first byte is now transferred. The Target will continue ask for additional bytes until the
entire Command Descriptor Block is transferred, and the Command Phase is ended.
-BSY
-SEL
-ATN
-MSG
-C/D
-I/O
-REQ
-ACK
min. 400 ns
1st comm. byte
Last comm. byte
min. 55 ns
min. 0 ns
min. 0 ns
-DB(0-7, P)
DB(8-15, P1)
Figure 8.5 Command Phase Sequence