MA28155
BIDIRECTIONAL BUS L/O CONTROL
Signal Definition (Mode 2)
INTR (Interrupt Request):
A high on this output can be used to interrupt the CPU for
both input or output operations.
Output Operations
OBFN
(Output Buffer Full):
The OBF output will go low to indicate that the CPU has
written data out to port A.
ACKN
(Acknowledge):
A low on this input enables the tri-state output buffer of port
A to send out the data. Otherwise, the output buffer will be in
the high impedance state,
INTE 1 (INTE register bit associated with OBFN):
Controlled by Bit Set/Reset of PC
6
.
Input Operations
STBN
(Strobe input):
A low on this input loads data in to the input latch,
IBF (Input Buffer Full Register Bit):
A high on this output indicates data has been loaded in to
the input latch,
INTE 2 (The INTE register bit associated with IBF).
Controlled by Bit Set/Reset of PC
4
.
OBF
A
N
ACK
A
N
STB
A
N
DSN
RD/WN
Figure 16: Mode 2 Bidirectional
11/20
DYNEX [ Dynex Semiconductor ]
