mc68hc912dg128 Freescale Semiconductor, Inc, mc68hc912dg128 Datasheet - Page 95

• Manufacturer Part Number: mc68hc912dg128
• Description: M68hc12 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Technical Data — MC68HC912DG128
6.1 Contents
6.2 Introduction
6.3 Detecting Access Type from External Signals
MC68HC912DG128 — Rev 3.0
MOTOROLA
6.2
6.3
6.4
Internally the MC68HC912DG128 has full 16-bit data paths, but
depending upon the operating mode and control registers, the external
multiplexed bus may be 8 or 16 bits. There are cases where 8-bit and
16-bit accesses can appear on adjacent cycles using the LSTRB signal
to indicate 8- or 16-bit data.
It is possible to have a mix of 8 and 16 bit peripherals attached to the
external multiplexed bus, using the NDRF bit in the MISC register while
in expanded wide modes.
The external signals LSTRB, R/W, and A0 can be used to determine the
type of bus access that is taking place. Accesses to the internal RAM
module are the only type of access that produce LSTRB = A0 = 1,
because the internal RAM is specifically designed to allow misaligned
16-bit accesses in a single cycle. In these cases the data for the address
Freescale Semiconductor, Inc.
For More Information On This Product,
Section 6. Bus Control and Input/Output
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Detecting Access Type from External Signals . . . . . . . . . . . . .95
Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Bus Control and Input/Output
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Technical Data
95