Freescale Semiconductor MCF51QE128RM Port a Data Register Ptad, Port a Pull Enable Register Ptape

Chapter 6 Parallel Input/Output Control

The PTA4 and PTA5 pins are unique. PTA4 is an output only, so the control bits for the input functions do not have any effect on this pin. PTA5, when configured as an output, is open drain. Therefore, the drive strength and slew rate controls have no effect on this pin.

6.7.1.1Port A Data Register (PTAD)

7 6 5 4

3 2 1 0

R

W

Reset:

PTAD7	PTAD6	PTAD5	PTAD41	PTAD3	PTAD2	PTAD1	PTAD0
0	0	0	0	0	0	0	0

1Reads of bit PTAD4 always return the contents of PTAD4, regardless of the value stored in the PTADD4 bit.

Figure 6-4. Port A Data Register (PTAD)

	Table 6-1. PTAD Register Field Descriptions
Field	Description
7–0	Port A Data Register Bits. For port A pins configured as inputs, reads return the logic level on the pin. For port A
PTADn	pins configured as outputs, reads return the last value written to this register.
	Writes are latched into all bits of this register. For port A pins configured as outputs, the logic level is driven out
	the corresponding MCU pin.
	Reset forces PTAD to all 0s, but these 0s are not driven out the corresponding pins because reset also configures
	all port pins as high-impedance inputs with pull-ups/pull-downs disabled.

6.7.1.2Port A Data Direction Register (PTADD)

7 6 5 4

3 2 1 0

R	PTADD7	PTADD6	PTADD5	PTADD41	PTADD3	PTADD2	PTADD1	PTADD0
W
Reset:	0	0	0	0	0	0	0	0

1PTADD4 has no effect on the output-only PTA4 pin.

Figure 6-5. Port A Data Direction Register (PTADD)

		Table 6-2. PTADD Register Field Descriptions
Field		Description
7–0	Data Direction for Port A Bits. These read/write bits control the direction of port A pins and what is read for PTAD
PTADDn	reads.
	0	Input (output driver disabled) and reads return the pin value.
	1	Output driver enabled for port A bit n and PTAD reads return the contents of PTADn.

6.7.1.3Port A Pull Enable Register (PTAPE)

The port A pull enable register enables pull-ups on the corresponding PTA pin. In some cases, a pull-down device is enabled if pull-downs are supported by an alternate pin function (e.g., KBI).

MCF51QE128 MCU Series Reference Manual, Rev. 3

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