Advanced Parallel I/O - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 308

MODE R EGISTER
This register establishes the operation mode and other miscellaneous functions (i.e., internal
visibility and emulation of Ports E and K). The contents of this register are shown in Figure 7.3.

7 6 5 4 3 2 1 0

MODC MODB MODA 0 IVIS 0 EMK EME

MODC, MODB, MODA: mode select bits
000 = special single-chip mode
001 = emulation narrow mode
010 = special test mode
011 = emulation wide mode
100 = normal single-chip mode
101 = normal expanded narrow mode (external memory data bus is 8-bit)
110 = special peripheral mode
111 = normal expanded wide mode (external memory data bus is 16-bit)
IVIS: internal visibility
0 = no visibility of internal bus operations on external bus.
1 = internal bus operations are visible on external bus.
EMK: emulate Port K
0 = PTK and DDRK are in memory map and port K can be used in general I/O.
1 = If in any expanded mode, PTK and DDRK are removed from memory map.
EME: emulate Port E
0 = PTE and DDRE are in the memory map so Port E can be used for general I/O.
1 = If in any expanded mode or special peripheral mode, PTE and DDRE are

removed from memory map, which allows the user to emulate the function

of these registers externalIy.

Figure 7.3 ■ The MODE register

P ULL -U P C ONTROL R EGISTER (PUCR)
This register is used to select the pull-up resistors for the pins associated with the core part.
The MC9S12DG256 has Ports A, B, E, and K in its core part. This register can be written any
time; its contents are shown in Figure 7.4.

7 6 5 4 3 2 1 0

Reset value
= 0x90

PUPKE 0 0 PUPEE 0 0 PUPBE PUPAE

PUPKE: Pull-up Port K enable
0 = pull-up resistors of Port K are disabled.
1 = pull-up resistors of Port K are enabled.
PUPEE: pull-up Port E enable
0 = pull-up resistors of Port E input pins 7 and 4-0 are disabled.
1 = pull-up resistors of Port E input pins 7 and 4-0 are enabled.
PUPBE: Pull-up Port B enable
0 = pull-up resistors of Port B are disabled.
1 = pull-up resistors of Port B are enabled.
PUPAE: Pull-up Port A enable
0 = pull-up resistors of Port A are disabled.
1 = pull-up resistors of Port A are enabled.

Figure 7.4 ■ Pull-Up Control register (PUCR)