Rabbit 3000 Microprocessor User's Manual

9. Parallel Ports

The Rabbit has seven 8-bit parallel ports designated A, B, C, D, E, F, and G. The pins used for the parallel ports are also shared with numerous other functions as shown in Table 5-2. The important properties of the ports are summarized below.

• Port A--Shared with the slave port data interface and auxiliary I/O data bus.

• Port B--Shared with control lines for slave port, auxiliary I/O address bus, and clock I/O for clocked serial mode option for Serial Ports A and B.

• Port C--Shared with serial port data I/O.

• Port D--4 bits shared with alternate I/O pins for Serial Ports A and B. 4 bits not shared. Port D can be configured as open drain outputs. Port D also contains output preload registers that can be clocked into the output registers under timer control for pulse generation.

• Port E--All bits of Port E can be configured as I/O strobes. 4 bits of port E can be used as external interrupt inputs. One bit of port E is shared with the slave port chip select. Port E has output preload registers that can be clocked into the output registers under timer control for pulse generation.

• Port F-- As outputs, Port F can be configured as open drain outputs. Alternatively, Parallel Port F outputs can carry the four Pulse-Width Modulator outputs. As inputs, Parallel Port F inputs can carry the inputs to the two channels of the quadrature decoders. Port F pins can also be configured to be used as clock pins for clocked Serial Ports C and D.

• Port G--As outputs, Port G can be configured as open drain outputs. Port G inputs and outputs are also used for access to other serial peripherals on the chip such as those used for asynchronous or SDLC/HDLC communication.

• Parallel Ports D-G behave in the same manner when used as digital I/O.

NOTE

There may be a conflict in using Parallel Port A and Parallel Port F. Either Parallel Port A can be used as inputs, in which case Parallel Port F has full function, or if Parallel Port A cannot be used as inputs, use any pins on Parallel Port F not used for PWM or serial clock outputs as inputs and take the precaution of setting up Parallel Port F before the conflicting functionality of Parallel Port A is enabled. Refer to Section 9.6.1, "Using Parallel Port A and Parallel Port F," for more information.

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) adr = 0x030	PA7	PA6	PA5	PA4	PA3	PA2	PA1	PA0

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.

9.2 Parallel Port B

Parallel Port B, has eight pins that can programmed individually to be inputs and outputs.

After reset, Parallel Port B comes up as six inputs (PB[5:0]) and two outputs (PB7 and PB6). The output value on pins PB6 and PB7 (package pins 99, 100) will be low.

Table 9-3. Parallel Port B Registers

Register Name	Mnemonic	I/O address	R/W	Reset
Port B Data Register	PBDR	0x40	R/W	00xxxxxx
Port B Data Direction Register	PBDDR	0x47	W	11000000

Table 9-4. Parallel Port B Register Bit Functions

	Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
PBDR (R/W) adr = 0x040	PB7	PB6	PB5	PB4	PB3	PB2	PB1	PB0
PBDDR (W) adr = 0x047	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out

When the auxiliary I/O bus is enabled, Parallel Port B bits 2:7 provide 6 address lines, the least significant 6 lines of the 16 lines that define the full I/O space.

When the slave port is enabled, parallel port lines PB2-PB7 are assigned to various slave port functions. However, it is still possible to read PB0-PB5 using the Port B data register even when lines PB2-PB7 are used for the slave port. It is also possible to read the signal driving PB6 and PB7 (this signal is on the signaling lines from the slave port logic).

Regardless of whether the slave port is enabled, PB0 reflects the input of the pin unless Serial Port B has its internal clock enabled, which causes this line to be driven by the serial port clock. PB1 reflects the input of the pin unless Serial Port A has its internal clock enabled.

• PBDR--Parallel Port B data register. Read/Write.

• PBDDR--Parallel Port B data direction register. A "1" makes the corresponding pin an output. This register is write only.

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 voltage 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) adr = 0x050	PC7 in	Echo drive	PC5 in	Echo drive	PC3 in	Echo drive	PC1 in	Echo drive
PCDR (w) adr = 0x050	x	PC6	x	PC4	x	PC2	x	PC0
PCFR (w) adr = 0x055	x	Drive TXA	x	Drive TXB	x	Drive TXC	x	Drive TXD

Parallel Port C shares its pins with serial ports A-D. The parallel port inputs can be configured 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.

9.4 Parallel Port D

Parallel Port D, shown in Figure 9-1, has eight pins that can be programmed individually to be inputs or outputs. When programmed as outputs, the pins can be individually selected to be open-drain outputs or standard outputs. Port D pins can be addressed by bit if desired. The output registers are cascaded and timer-controlled, making it possible to generate precise timing pulses. Port D bits 4 and 5 can be used as alternate bits for Serial Port B, and bits 6 and 7 can be used as alternate bits for Serial Port A. Alternate serial port bit assignments make it possible for the same serial port to connect to different communications lines that are not operating at the same time.

On reset, the data direction register is zeroed, making all pins inputs. In addition certain bits in the control register are zeroed (bits 0,1,4,5) to ensure that data is clocked into the output registers when loaded. All other registers associated with port D are not initialized on reset.

Table 9-7. Parallel Port D Registers

Register Name	Mnemonic	I/O address	R/W	Reset
Port D Data Register	PDDR	0x60	R/W	xxxxxxxx
Port D Control Register	PDCR	0x64	W	xx00xx00
Port D Function Register	PDFR	0x65	W	xxxxxxxx
Port D Drive Control Register	PDDCR	0x66	W	xxxxxxxx
Port D Data Direction Register	PDDDR	0x67	W	00000000
Port D Bit 0 Register	PDB0R	0x68	W	xxxxxxxx
Port D Bit 1 Register	PDB1R	0x69	W	xxxxxxxx
Port D Bit 2 Register	PDB2R	0x6A	W	xxxxxxxx
Port D Bit 3 Register	PDB3R	0x6B	W	xxxxxxxx
Port D Bit 4 Register	PDB4R	0x6C	W	xxxxxxxx
Port D Bit 5 Register	PDB5R	0x6D	W	xxxxxxxx
Port D Bit 6 Register	PDB6R	0x6E	W	xxxxxxxx
Port D Bit 7 Register	PDB7R	0x6F	W	xxxxxxxx

Figure 9-1. Parallel Port D Block Diagram

Table 9-8. Parallel Port D Register functions

	Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
PDDR (R/W) adr = 0x060	PD7	PD6	PD5	PD4	PD3	PD2	PD1	PD0
PDDCR (W) adr = 0x066	out = open drain	out = open drain	out = open drain	out = open drain	out = open drain	out = open drain	out = open drain	out = open drain
PDFR (W) adr = 0x065	x	alt TXA	x	alt TXB	x	x	x	x
PDDDR (W) adr = 0x067	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out
PDB0R (W) adr = 0x068	x	x	x	x	x	x	x	PD0
PDB1R (W) adr = 0x069	x	x	x	x	x	x	PD1	x
PDB2R (W) adr =0x 06A	x	x	x	x	x	PD2	x	x
PDB3R (W) adr = 0x06B	x	x	x	x	PD3	x	x	x
PDB4R (W) adr = 0x06C	x	x	x	PD4	x	x	x	x
PDB5R (W) adr = 0x06D	x	x	PD5	x	x	x	x	x
PDB6R (W) adr = 0x06E	x	PD6	x	x	x	x	x	x
PDB7R (W) adr = 0x06F	PD7	x	x	x	x	x	x	x

Table 9-9. Parallel Port D Control Register (adr = 0x064)

Bits 7, 6	Bits 5, 4	Bits 3, 2	Bits 1, 0
x,x	00--clock upper nibble on pclk/2 01--clock on timer A1 10--clock on timer B1 11--clock on timer B2	x,x	00--clock lower nibble on pclk/2 01--clock on timer A1 10--clock on timer B1 11--clock on timer B2

The following registers are described in Table 9-8 and in Table 9-9.

• PDDR--Parallel Port D data register. Read/Write.

• PDDDR--Parallel Port D data direction register. A "1" makes the corresponding pin an output. Write only.

• PDDCR--Parallel Port D drive control register. A "0" makes the corresponding pin a regular output. A "1" makes the corresponding pin an open-drain output. Write only.

• PDFR--Parallel Port D function control register. This port may be used to make port positions 4 and 6 be serial port outputs. Write only.

• PDBxR--These eight registers may be used to set outputs on individual port positions.

• PDCR--Parallel Port D control register. This register is used to control the clocking of the upper and lower nibble of the final output register of the port. On reset, bits 0, 1, 4, and 5 are reset to zero.

9.5 Parallel Port E

Parallel Port E, shown in Figure 9-2, has eight I/O pins that can be individually programmed as inputs or outputs. PE7 is used as the slave port chip select when the slave port is enabled. Each of the port E outputs can be configured as an I/O strobe. In addition, four of the port E lines can be used as interrupt request inputs. The output registers are cascaded and timer-controlled, making it possible to generate precise timing pulses.

Figure 9-2. Parallel Port E Block Diagram

Table 9-10. Parallel Port E Registers

Register Name	Mnemonic	I/O address	R/W	Reset
Port E Data Register	PEDR	0x70	R/W	xxxxxxxx
Port E Control Register	PECR	0x74	W	xx00xx00
Port E Function Register	PEFR	0x75	W	00000000
Port E Data Direction Register	PEDDR	0x77	W	00000000
Port E Bit 0 Register	PEB0R	0x78	W	xxxxxxxx
Port E Bit 1 Register	PEB1R	0x79	W	xxxxxxxx
Port E Bit 2 Register	PEB2R	0x7A	W	xxxxxxxx
Port E Bit 3 Register	PEB3R	0x7B	W	xxxxxxxx
Port E Bit 4 Register	PEB4R	0x7C	W	xxxxxxxx
Port E Bit 5 Register	PEB5R	0x7D	W	xxxxxxxx
Port E Bit 6 Register	PEB6R	0x7E	W	xxxxxxxx
Port E Bit 7 Register	PEB7R	0x7F	W	xxxxxxxx

The following registers are described in Table 9-11 and in Table 9-12.

• PEDR--Port E data register. Reads value at pins. Writes to port E preload register.

• PEDDR--Port E data direction register. Set to "1" to make corresponding pin an output. This register is zeroed on reset.

• PEFR--Port E function register. Set bit to "1" to make corresponding output an I/O strobe. The nature of the I/O strobe is controlled by the I/O bank control registers (IBxCR). The data direction must be set to output for the I/O strobe to work.

• PEBxR--These are individual registers to set individual output bits on or off.

• PECR--Parallel Port E control register. This register is used to control the clocking of the upper and lower nibble of the final output register of the port. On reset, bits 0, 1, 4, and 5 are reset to zero.

On reset, the data direction register and function register are zeroed, making all pins inputs, and disabling the alternate output functions. In addition certain bits in the control register are zeroed (bits 0,1,4,5) to ensure that data is clocked into the output registers when loaded. All other registers associated with Port E are not initialized on reset.

Table 9-11. Parallel Port E Register functions

	Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
PEDR (R/W) adr = 0x070	PE7	PE6	PE5	PE4	PE3	PE2	PE1	PE0
PEFR (W) adr = 0x075	alt /I7	alt /I6	alt /I5	alt /I4	alt /I3	alt /I2	alt /I1	alt /I0
PEDDR (W) adr = 0x077	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out
PEB0R (W) adr = 0x078	x	x	x	x	x	x	x	PE0
PEB1R (W) adr = 0x079	x	x	x	x	x	x	PE1	x
PEB2R (W) adr = 0x07A	x	x	x	x	x	PE2	x	x
PEB3R (W) adr = 0x07B	x	x	x	x	PE3	x	x	x
PEB4R (W) adr = 0x07C	x	x	x	PE4	x	x	x	x
PEB5R (W) adr = 0x07D	x	x	PE5	x	x	x	x	x
PEB6R (W) adr = 0x07E	x	PE6	x	x	x	x	x	x
PEB7R (W) adr = 0x07F	PE7	x	x	x	x	x	x	x

Table 9-12. Parallel Port E Control Register (adr = 0x074)

Bits 7, 6	Bits 5, 4	Bits 3, 2	Bits 1, 0
x,x	00--clock upper nibble on pclk/2 01--clock on timer A1 10--clock on timer B1 11--clock on timer B2	x,x	00--clock lower nibble on pclk/2 01--clock on timer A1 10--clock on timer B1 11--clock on timer B2

9.6 Parallel Port F

Parallel Port F is a byte-wide port with each bit programmable for data direction and drive. These are simple inputs and outputs controlled and reported in the Port F Data Register. As outputs, the bits of the port are buffered, with the data written to the Port F Data Register transferred to the output pins on a selected timing edge. The outputs of Timer A1, Timer B1, or Timer B2 can be used for this function, with each nibble of the port having a separate select field to control this timing.

These inputs and outputs are also used for access to other peripherals on the chip. As outputs, the Parallel Port F outputs can carry the four Pulse-Width Modulator outputs. As inputs, Parallel Port F inputs can carry the inputs to the quadrature decoders. When Serial Port C or Serial Port D is used in the clocked serial mode, two pins of Parallel Port F are used to carry the serial clock signals. When the internal clock is selected in these serial ports, the corresponding bit of Parallel Port F is set as an output.

The Parallel Port F registers and their functions are described in Table 9-14 and in Table 9-15.

Table 9-13. Parallel Port F Registers

Register Name	Mnemonic	I/O address	R/W	Reset
Port F Data Register	PFDR	0x38	R/W	xxxxxxxx
Port F Control Register	PFCR	0x3C	W	xx00xx00
Port F Function Register	PFFR	0x3D	W	xxxxxxxx
Port F Drive Control Register	PFDCR	0x3E	W	xxxxxxxx
Port F Data Direction Register	PFDDR	0x3F	W	00000000

Table 9-14. Parallel Port F Register Functions

	Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
PFDR (R/W) adr = 0x038	PF7	PF6	PF5	PF4	PF3	PF2	PF1	PF0
PFFR (W) adr = 0x03D	pwm[3]	pwm[2]	pwm[1]	pwm[0]	x	x	sclk_c	sclk_d
PFDCR (W) adr = 0x03E	out = open drain	out = open drain	out = open drain	out = open drain	out = open drain	out = open drain	out = open drain	out = open drain
PFDDR (W) adr = 0x03F	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out

Table 9-15. Parallel Port F Control Register (adr = 0x03C)

Bits 7, 6	Bits 5, 4	Bits 3, 2	Bits 1, 0
x,x	00--clock upper nibble on pclk/2 01--clock on timer A1 10--clock on timer B1 11--clock on timer B2	x,x	00--clock lower nibble on pclk/2 01--clock on timer A1 10--clock on timer B1 11--clock on timer B2

The following registers are described in Table 9-14 and in Table 9-15.

• PFDR--Port F data register. Reads value at pins. Writes to port F preload register.

• PFCR--Parallel Port F control register. This register is used to control the clocking of the upper and lower nibble of the final output register of the port. On reset, bits 0, 1, 4, and 5 are reset to zero.

• PFFR--Port F function register. Set bit to "1" to enable alternate output function. Bits 7-4 enable the PWM outputs and bits 1-0 enable synchronous serial ports C and D clock outputs for when the serial port is configured for internal clock generation.

• PFDCR--Parallel Port F drive control register. A "0" makes the corresponding pin a regular output. A "1" makes the corresponding pin an open-drain output. Write only.

• PFDDR--Port F data direction register. Set to "1" to make corresponding pin an output. This register is zeroed on reset.

On reset, the data direction register is zeroed, making all pins inputs. In addition certain bits in the control register are zeroed (bits 0,1,4,5) to ensure that data is clocked into the output registers when loaded. All other registers associated with port F are not initialized on reset.

9.6.1 Using Parallel Port A and Parallel Port F

A bug has been discovered in the Rabbit 3000 that results in a conflict between Parallel Port F and Parallel Port A under certain conditions. This bug has been corrected in versions of the Rabbit chip designated 3000A and later. See Appendix B for further details.

The bug is rooted in an incomplete address decode for the data output register for Parallel Port A. This register responds to any of 16 addresses 30 to 3F (hex). When Parallel Port F was added, the addresses 38 to 3F were used, and the decode for Parallel Port A was not updated.

There are five registers in Parallel Port F at addresses in the range of 38 to 3F. Writing to any of these registers will also cause a write to the Parallel Port A output register, which is identical to the slave port number zero output register. If Parallel Port A is used as in input register or if the auxiliary I/O bus (which uses the pins of Parallel Port A as a data bus) is enabled, then the spurious write has no effect on operation because the Parallel Port A output register is not used. However if Parallel Port A is used as an output or is used as the bidirectional bus of the slave port, then writing to any of the Parallel Port F registers will cause a spurious write to the Parallel Port A register, which will have a spurious effect on the operation of the Rabbit 3000 chip.

The functionality of the Parallel Port F pins is not affected for pulse width modulation outputs and serial clock outputs, except that the Parallel Port F function and direction registers should be set up before a conflicting function on Parallel Port A is in use, since writing to these registers also writes to the Parallel Port A output register.

9.6.1.1 Summary

Parallel Port A	Parallel Port F
Parallel Inputs	Full Functionality
Parallel Outputs	Parallel Inputs, PWM, Serial Port Clocks
Slave Port	Parallel Inputs, PWM, Serial Port Clocks
Auxiliary I/O Bus	Full Functionality

• If you enable the auxiliary I/O bus, which uses Parallel Port A, then the bug does not manifest itself and you can use the full functionality of Parallel Port F.

• If you use Parallel Port A as inputs, then the bug does not manifest itself and the full functionality of Parallel Port F is available.

• If you use Parallel Port A as outputs, then you cannot use Parallel Port F pins as outputs too, except that you can use the PWM and clock outputs provided that you are aware that writing to the control registers of Parallel Port F will also write to the data output register of Parallel Port A. A simple way to resolve this is to leave Parallel Port A as an input until you complete the setup of Parallel Port F and then switch Parallel Port A to be an output. You can always use pins on Parallel Port F as inputs.

• If you enable the slave port, then you cannot use Parallel Port F as parallel outputs, but you can still use the other output functions of Parallel Port F following the precautions regarding setup described above.

The easiest approach to avoid any problem when there is a conflict is to assign inputs and outputs in such a manner as to avoid the bug. Either Parallel Port A can be used as inputs, in which case Parallel Port F has full function, or if Parallel Port A cannot be used as inputs, use any pins on Parallel Port F not used for PWM or serial clock outputs as inputs and take the precaution of setting up Parallel Port F before the conflicting functionality of Parallel Port A is enabled.

9.7 Parallel Port G

Parallel Port G is a byte-wide port with each bit programmable for data direction and drive. These are simple inputs and outputs controlled and reported in the Port G Data Register. As outputs, the bits of the port are buffered, with the data written to the Port G Data Register transferred to the output pins on a selected timing edge. The outputs of Timer A1, Timer B1, or Timer B2 can be used for this function, with each nibble of the port having a separate select field to control this timing.

These inputs and outputs are also used for access to other peripherals on the chip. As outputs, Port G can carry the data and clock outputs from Serial Ports E and F. As inputs, Port G can carry the data and clock inputs for these two serial ports.

The following registers are described in Table 9-17 and in Table 9-18.

Table 9-16. Parallel Port G Registers

Register Name	Mnemonic	I/O address	R/W	Reset
Port G Data Register	PGDR	0x48	R/W	xxxxxxxx
Port G Control Register	PGCR	0x4C	W	xx00xx00
Port G Function Register	PGFR	0x4D	W	xxxxxxxx
Port G Drive Control Register	PGDCR	0x4E	W	xxxxxxxx
Port G Data Direction Register	PGDDR	0x4F	W	00000000

Table 9-17. Parallel Port G Data Register Functions

	Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
PGDR (R/W) adr = 0x048	PG7	PG6	PG5	PG4	PG3	PG2	PG1	PG0
PGFR (W) adr = 0x04D	x	SOUT_E	RCLK_E	TCLK_E	x	SOUT_F	RCLK_F	TCLK_F
PGDCR (W) adr = 0x04E	out = open drain	out = open drain	out = open drain	out = open drain	out = open drain	out = open drain	out = open drain	out = open drain
PGDDR (W) adr = 0x04F	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out	dir = out

Table 9-18. Parallel Port G Control Register (adr= 0x04C)

Bits 7, 6	Bits 5, 4	Bits 3, 2	Bits 1, 0
x,x	00--clock upper nibble on pclk/2 01--clock on timer A1 10--clock on timer B1 11--clock on timer B2	x,x	00--clock lower nibble on pclk/2 01--clock on timer A1 10--clock on timer B1 11--clock on timer B2

The following registers are described in Table 9-17 and in Table 9-18.

• PGDR--Port G data register. Reads value at pins. Writes to port G preload register.

• PGCR--Parallel Port G control register. This register is used to control the clocking of the upper and lower nibble of the final output register of the port. On reset, bits 0, 1, 4, and 5 are reset to zero.

• PGFR--Port G function register. Set bit to "1" to enable alternate output function. Bits 6 and 2 enable the asycnhronous or SDLC/HDLC serial ports E and F outputs. And bits 5-4 and 1-0 enable the SDLC/HDLC transmit and receive clock outputs for serial ports E and F.

• PGDCR--Parallel Port G drive control register. A "0" makes the corresponding pin a regular output. A "1" makes the corresponding pin an open-drain output. Write only.

• PGDDR--Port G data direction register. Set to "1" to make corresponding pin an output. This register is zeroed on reset.

On reset, the data direction register is zeroed, making all pins inputs. In addition certain bits in the control register are zeroed (bits 0,1,4,5) to ensure that data is clocked into the output registers when loaded. All other registers associated with port G are not initialized on reset.