Jameco Electronics 2000 Parallel Port C Registers, Parallel Port C Register Bit Functions

9.3 Parallel Port C

Parallel Port C, shown in Table 9-6,has four inputs and four outputs. The even-numbered ports, PC0, PC2, PC4, and PC6, are outputs. The odd-numbered ports, PC1, PC3, PC5, and PC7, are inputs. When the data register is read, bits 1,3,5,7 return the value of the volt- age on the pin. Bits 0,2,4,6 return the value of the signal driving the output buffers. The signal driving the output buffers and the value of the output pin are normally the same. Either the Port C data register is driving these pins or one of the serial port transmit lines is driving the pin. The bits set in the PCFR Parallel Port C Function Register identify whether the data register or the serial port transmit lines were driving the pins.

Table 9-5. Parallel Port C Registers

Register Name	Mnemonic	I/O address	R/W	Reset
Port C Data Register	PCDR	0x50	R/W	x0x1x1x1
Port C Function Register	PCFR	0x55	W	x0x0x0x0

Table 9-6. Parallel Port C Register Bit Functions

	Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
PCDR (r)	PC7 in	Echo	PC5 in	Echo	PC3 in	Echo	PC1 in	Echo
adr = 0x050		drive		drive		drive		drive
PCDR (w)	x	PC6	x	PC4	x	PC2	x	PC0
adr = 0x050
PCFR (w)	x	Drive	x	Drive	x	Drive	x	Drive
adr = 0x055		TXA		TXB		TXC		TXD

Parallel Port C shares its pins with serial ports A-D. The parallel port inputs can be config- ured as serial port inputs while the dedicated outputs as serial port outputs.

When serving as serial inputs, the data lines can still be read from the Parallel Port C data register. The parallel port outputs can be selected to be serial port outputs by setting the corresponding bit positions in the Port C Function register (PCFR). When a parallel port output pin is selected to be a serial port output, the value stored in the data register is ignored.

On reset the active (even-numbered) function register bits are zeroed resulting in Port C to behave as an I/O port. Bit 6 of the Port C data register is zeroed while the remaining even numbered bits are set to 1.

132 Rabbit 3000 Microprocessor