Hardware Reference
In-Depth Information
RESET signal, the state of the PK7 pin is latched to the ROMON bit of the MISC register. If this
bit is 1, the on-chip flash memory is enabled in the expanded mode. This bit is forced to 1 in
single-chip modes.
Port T has a port I/O register (PTT), port data direction register (DDRT), port input regis-
ter (PTIT), reduced drive register (RDRT), pull device enable register (PERT), and port polarity
select register (PPST).
The PTIT register allows us to read back the status of Port T pins. This register can also be
used to detect overload or short circuit conditions on output pins. Reading the port data register
achieves the same purpose.
The RDRT register configures the drive strength of each port T output pin as either full or
reduced current. If a port T pin is used as input, this bit is ignored. The reduced drive feature for
each pin can be enabled individually. The contents of RDRT are shown in Figure 7.7.
0
7
6
5
4
3
2
1
Reset value
= 0x00
RDRT7
RDRT6
RDRT5
RDRT4
RDRT3
RDRT2
RDRT1 RDRT0
RDRT[7:0]: reduced drive Port T
0 = full drive strength at output.
1 = associated pin drives at about 1/3 of the full drive strength.
Figure 7.7
■
Port T Reduced Drive register (RDRT)
The PERT register configures whether a pull-up or pull-down device is enabled if the port is
used as input. Each pin's pull-up or pull-down device can be enabled individually. No pull-up or
pull-down device is enabled out of reset. The contents of PERT are shown in Figure 7.8.
7
6
5
4
3
2
1
0
Reset value
= 0x00
PERT7
PERT6
PERT5
PERT4
PERT3
PERT2
PERT1
PERT0
PERT[7:0]: pull device enable Port T
0 = pull-up or pull-down is disabled.
1 = either pull-up or pull-down is enabled.
Figure 7.8
■
Port T Pull Device Enable register (PERT)
The PPST register selects whether a pull-down or a pull-up device is connected to the pin.
This register has an effect on input pins only. The contents of PPST are shown in Figure 7.9.
7
6
5
4
3
2
1
0
Reset value
= 0x00
PPST7
PPST6
PPST5
PPST4
PPST3
PPST2
PPST1
PPST0
PPST[7:0]: pull device enable Port T
0 = a pull-up device is connected to the associated Port T pin, if enabled
by the associated bit in register PERT and if the port is used as input
or as wired-OR output.
1 = a pull-down device is connected to the associated Port T pin, if enabled
by the associated bit in register PERT and if the port is used as input.
Figure 7.9
■
Port T Polarity Select register (PPST)
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