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4.2.2 Bus signals
Table 4-2 Bus signals
Signal name Type of signal Initiator
⇐
⇒
Target
Data DB0
DB1
DB2
DB3
DB4
DB5
DB6
DB7
(Data Bus n)
DBP
(Data Bus Parity)
Eight data-bit signals, plus a parity-bit signal that forms a DATA
BUS. DB(7) is the most significant bit and has the highest
priority during the ARBITRATION phase. Bit number,
significance and priority decease downward to DB(O). A data bit
is defined as one when the signal value is true. A data bit is
defined as zero when the signal value is false. Data parity DB(P)
shall be odd. Parity is undefined during the ARBITRATION
phase.
⇐
⇒
Control Signals BSY (Busy)
An "ORtied" signal that indicates that the bus is being used
⇐
⇒
SEL (Select)
An "ORtied" signal used either by an initiator to select a target or
by a target to reselect an initiator
⇐
⇒
RST (reset) An "ORtied" signal that indicates the RESET condition
⇐
⇒
C/D (Control/Data)
I/O (Input/Output)
MSG Message
The C/D, I/O, and MSG signals are used to distinguish between
the different information transfer phases.
⇐
REQ (request) A signal driven by an initiator to indicate a request for a
REQ/ACK data transfer handshake
⇐
ACK (acknowledge) A signal driven by an initiator in indicate and acknowledgment
for REQ/ACK data transfer handshake.
⇒
ATN (Attention) A signal driven by an initiator to indicate the ATTENTION
condition
⇒