4-7
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
⇒
