Jameco Electronics 2000, 3000 manual Parallel Port A

9.1 Parallel Port A

Parallel Port A has a single read/write register:

Table 9-1. Parallel Port A Registers

Register Name	Mnemonic	I/O address	R/W	Reset
Port A Data Register	PADR	0x30	R/W	xxxxxxxx
Slave Port Control Register	SPCR	0x24	R/W	0xx00000

Table 9-2. Parallel Port A Data Register Bit Functions

	Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
PADR (R/W)	PA7	PA6	PA5	PA4	PA3	PA2	PA1	PA0
adr = 0x030

This register should not be used if the slave port or auxiliary I/O bus is enabled.

The slave port control register is used to control whether Parallel Port A is configured as slave databus, auxiliary I/O data bus, parallel Input or parallel output. To make the port an input, store 0x080 in the SPCR (slave port control register). To make the port an output, store 0x084 in SPCR. Parallel Port A is set up as an input port on reset.

When the port is read, the value read reflects the voltages on the pins, "1" for high and "0" for low. This could be different than the value stored in the output register if the pin is forced to a different state by an external voltage.

NOTE: Refer to Section 9.6.1, “Using Parallel Port A and Parallel Port F,” for more information.

130 Rabbit 3000 Microprocessor