4.2.2
Bus signals
Signal name
Data
DB0
DB1
DB2
DB3
DB4
DB5
DB6
DB7
(Data Bus n)
DBP
(Data Bus
Parity)
Control
BSY
signals
(Busy)
SEL
(Select)
RST
(Reset)
C/ D
(Control/Data)
I/ O
(Input/Output)
MSG
(Message)
REQ
(Request)
ACK
(Acknowledge)
ATN
(Attention)
Type of signal
Eight data>bit signals, plus a parity>bit signal
that form a DATA BUS. DB(7) is the most
significant bit and has the highest priority during
the ARBITRATION phase. Bit number,
significance, and priority decrease downward to
DB(0).
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.
An ™ORtied∫ signal that indicates that the bus is
being used
An ™ORtied∫ signal used either by an initiator to
select a target or by a target to reselect an
initiator
An ™ORtied∫ signal that indicates the RESET
condition
The C/D, I/O, and MSG signals are used to
distinguish between the different information
transfer phases.
During an information transfer phase, the target
uses this signal to request the initiator to transfer
data
A signal driven by an initiator to indicate an
acknowledgement for REQ/ACK data transfer
handshake
A signal driven by an initiator to indicate the
ATTENTION condition
Initiator
Target
4 $ 7