Overview Of I/O Ports - Fujitsu MB91260B Series Hardware Manual

CHAPTER 4 I/O PORTS
4.1

Overview of I/O Ports

This LSI can use its pins as I/O ports when they are set not to serve for input to or
output from their respective external bus interfaces or peripherals.
■ Basic Block Diagram of I/O Ports
An I/O port with pull-up resistor comprises the following registers:
• PDR (Port Data Register)
• DDR (Data Direction Register)
• PFR (Port Function Register)
• PCR (Pull-up Control Register)
The following diagram shows a basic configuration of an I/O port.
Port Bus
Peripheral output
■ Mode for I/O Ports
●
In port input mode (PFR=0 & DDR=0)
PDR read: The level at the corresponding external pin is read.
PDR write:A setting value is written to the PDR.
●
In port output mode (PFR=0 & DDR=1)
PDR read: The PDR value is read.
PDR write:The PDR value is output to the corresponding external pin.
102
Figure 4.1-1 Basic Block Diagram of I/O Ports
PDR read
1
PDR
0
PFR
DDR
PCR
PCR = 0: No pull-up resistor
PCR = 1: Pull-up resistor provided
Peripheral input
0
1
DDR: Data Direction Register
PDR: Port Data Register
PFR: Port Function Register
PCR: Pull-up Control Register
Pull-up resistor
(About 50 kΩ)
Pin