Hardware manual

Rev. 3.0, 09/98, page 113 of 361
6.9 Port 8
Port 8 is a 7-bit input/output port that also provides pins for interrupt input and serial
communication. Table 6.19 lists the pin functions.
Table 6.19 Port 8 Pin Functions
Pin I/O Port Serial Communication Interrupt Input
P8
0
Input/output 
P8
1
Input/output 
P8
2
Input/output 
P8
3
Input/output 
P8
4
Input/output TxD
1
output IRQ
3
input
P8
5
Input/output RxD
1
input IRQ
4
input
P8
6
Input/output SCK
1
input/output IRQ
5
input
Pins of port 8 can drive a single TTL load and a 30pF capacitive load when they are used as output
pins. They can also drive a Darlington pair.
Table 6.20 details the port 8 registers.
Table 6.20 Port 8 Registers
Name Abbreviation Read/Write Initial Value Address
Port 8 data direction register P8DDR W H'80 H'FFBD
Port 8 data register P8DR R/W H'80 H'FFBF
Port 8 Data Direction Register (P8DDR)H'FFBD
Bit:76543210
P8
6
DDR P8
5
DDR P8
4
DDR P8
3
DDR P8
2
DDR P8
1
DDR P8
0
DDR
Initial value:10000000
Read/Write:  WWWWWWW
P8DDR is an 8-bit register that selects the direction of each pin in port 8. A pin functions as an
output pin if the corresponding bit in P8DDR is set to “1,” and as in input pin if the bit is cleared
to “0.”
Bit 7 is reserved. It cannot be modified, and is always read as “1.”