CHAPTER 5 PORT FUNCTIONS
152
5.11 Port 9
Port 9 is a 5-bit I/O port with an output latch. This port can be set in the input or output mode in 1-bit units by using port
9 mode register (PM9). Each pin is provided with a software programmable pull-up resistor.
In addition to the I/O port function, port 9 also functions as control signal pins (refer to
Table 5-9
). P90 through P93
functions as a read/write strobe signals and address strobe signal when an external memory or I/O is connected. P94
functions as a wait signal input pin if so specified by port 9 mode control register (PMC9).
When RESET is input, this port is set in the input mode (output high-impedance status), and the contents of the output
latch are undefined.
Table 5-9. Operation Mode of Port 9
Pin Name
Port Mode
Control Signal I/O Mode
Manipulation to Use Port 9 as Control Pins
P90
I/O Port
RD
Specifying external memory expansion mode by
P91
LWR
MM0 through MM3 bits of memory expansion
P92
HWR
mode register (MM)
P93
ASTB
P94
WAIT
Setting of PMC94 bit of PMC9 to 1
Remark
For details, refer to
CHAPTER 17 LOCAL BUS INTERFACE FUNCTION
.
(a) Port mode
Each port pin not set in the control mode can be set in the input or output mode in 1-bit units by using the port
9 mode register (PM9).
(b) Control signal I/O mode
(i) RD (Read Strobe)
This pin outputs a strobe signal to read an external memory. The operation of this pin is specified by the
memory expansion mode register (MM).
(ii) LWR, HWR (Low/High Write Strobe)
These pins output strobe signals to write an external memory. The operations of these pins are specified
by the memory expansion mode register (MM).
(iii) ASTB (Address Strobe)
This is a timing signal output pin to latch the address information output from the AD0 through AD15 pins
to access the external memory. The operation of this pin is specified by the memory expansion mode
register (MM).
(iv) WAIT (Wait)
This pin inputs a wait signal. The operation of this pin is specified by the port 9 mode control register (PMC9).