
Rev.2.00
Aug 28, 2006
page 111 of 148
7641 Group
REJ09B0336-0200
APPLICATION
2.8 Master CPU bus interface
2.8.3 Functional description
The internal 2-byte bus interface can be controlled by the signals from the host CPU side; it is called the
slave mode. This bus interface allows the 7641 group to be directly connected with a R/W type of CPU
bus or a RD and WR separate type of CPU bus.
Ports P52 to P57, P60 to P67, P72 to P74 become the master CPU bus interface function pins when the
master CPU bus interface is enabled.
P60 to P67: Function as data I/O pins (DQ0 to DQ7). (Be sure to set them to input mode by setting the port
P6 direction register to “0”.)
P52, P74: Function as the status signal OBFx (x = 0, 1). The state of the output buffer DBBx (x = 0, 1) is
output.
P53, P73: Function as the status signal IBFx (x = 0, 1). The state of the input buffer DBBx (x = 0, 1) is
output.
P54, P72: Function as the status signal Sx (x = 0, 1). The chip select signals from the host CPU are input.
P55: Functions as the status signal A0. When A0 is “H”, the host CPU can read the contents of the data
bus buffer status register x (x = 0, 1) (addresses 4916, 4D16). When A0 is “L”, the contents of data bus
buffer register x (x = 0, 1) can be output owing to a read request from the host CPU.
When a data is written into the data bus buffer register x (x = 0, 1), if A0 is “L”, this indicates that its
contents are the data; if “H”, this indicates that they are the command.
P72 to P74 become the master CPU bus interface function pins only when the double data bus buffer mode
is used.
Tables 2.8.1 and 2.8.2 shows the bus control signal and data bus state; Figure 2.8.6 shows a connection
example.
Sx signal
L
H
RD signal
L
H
–
WR signal
H
L
–
A0 signal
L
H
L
H
–
Data bus state
Read
Write
High-impedance
Data on data bus
Output data
DBBSx contents
Input data (data)
Input data (command)
–
Table 2.8.1 Bus control signal and data bus state-RD/WR separate type
Sx signal
L
H
R/W signal
H
L
–
E signal
H
–
A0 signal
L
H
L
H
–
Data bus state
Read
Write
High-impedance
Data on data bus
Output data
DBBSx contents
Input data (data)
Input data (command)
–
Table 2.8.2 Bus control signal and data bus state-R/W type