M68HC16 Z SERIES
CENTRAL PROCESSOR UNIT
USER’S MANUAL
4-7
Signed 36-bit fixed-point numbers are used only by the MAC unit. Bit 35 is the sign bit.
Bits [34:31] are sign extension bits. There is an implied radix point between bits 31 and
30. There are 31 bits of magnitude, but use of the extension bits allows representation
of numbers in the range –16 ($800000000) to 15.999969482 ($7FFFFFFFF).
4.5 Memory Organization
Both program and data memory are divided into sixteen 64-Kbyte banks. Addressing
is linear. A 20-bit extended address can access any byte location in the appropriate
address space.
A word is composed of two consecutive bytes. A word address is normally an even
byte address. Byte 0 of a word has a lower 16-bit address than byte 1. Long words and
32-bit signed fractions consist of two consecutive words, and are normally accessed
at the address of byte 0 in word 0.
Instruction fetches always access word addresses. Word operands are normally ac-
cessed at even byte addresses, but can be accessed at odd byte addresses, with a
substantial performance penalty.
To permit compatibility with the M68HC11, misaligned word transfers and misaligned
stack accesses are allowed. Transferring a misaligned word requires two successive
byte transfer operations.
shows how each CPU16 data type is organized in memory. Consecutive
even addresses show size and alignment.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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