10-6 MC68VZ328 User’s Manual
Programming Model

10.3.4 Port Pull-up and Pull-down Resistors

The pull-up and pull-down resistors are enabled by setting t he pull -up or pu ll-dow n enable r egister ’s bits to
1. Pull-up and pull-down resistors can be selected individually regardless of whether the I/O port is
selected or not. After reset, Ports A–F, J, K, and M default to the I/O function with internal pull-up or
pull-down enabled. Resistor assignments for individual ports is shown in Table10-3. Meanwhile, Port G
defaults to the dedicated function, except for the HIZ/P/D/PG3 pin, which defaults to the PG3 function.
10.4 Programming Model
The chapter’s remaining sections provide programming information about individual ports.

10.4.1 Port A Registers

The Port A registers are general-purpose 8-bit I/O registers. They consist of the following:
Port A direction register (PADIR)
Port A data register (PADATA)
Port A pull-up enable register (PAPUEN)
Port A functions either as a GPIO (PA[7:0]) or the lower data byte of the data bus (D[7:0]). Port A can be
used as PA[7:0] only when the MC68VZ328 is operating as an 8-bit system by setting the WDTH8 bit in
the system control register (0xFFFFF000). If the MC68VZ328 is operat ing i n eit her 16-bit or mixed 8 - and
16-bit systems, the pins only function as D[7:0].
At reset the WDTH8 bit of the SCR is cleared, resulting in Port A becoming t he lower data byte of th e data
bus (D[7:0]) with internal pull-up resistors enabled.
In sleep mode, all of the data bus pins (D[15:0]) are individually pulled up with 1 Mresistors.
Table 10-3. Pull-up and Pull-down Resistors by Port
Port Pull-up Pull-down
A, B, D, E, G, and J All bits None
C None All bits
FBits 7, 2–0 Bits 6–3
K Bits 3–0 Bits 7–4
MBit 5Bits 40