Debug Support
MOTOROLA
ColdFire2/2M User’s Manual
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7-11
R/W Field
The R/W field specifies the direction of operand transfer. When the bit is set, the transfer is
from the CPU to the development system. When the bit is cleared, data is written to the CPU
or to memory from the development system.
Operand Size
For sized operations, this field specifies the operand data size. All addresses are expressed
as 32-bit absolute values. The size field is encoded as listed in
Table 7-4
.
Address / Data (A/D) Field
The A/D field is used in commands that operate on address and data registers in the
processor. It determines whether the register field specifies a data or address register. A one
indicates an address register; zero, a data register.
Register Field
In commands that operate on processor registers, this field specifies which register is
selected. The field value contains the register number.
Extension Word(s) (as required):
Certain commands require extension words for addresses and/or immediate data.
Addresses require two extension words because only absolute long addressing is permitted.
Immediate data can be either one or two words in length—byte and word data each require
a single extension word; longword data requires two words. Both operands and addresses
are transferred most significant word first. In the following descriptions of the BDM command
set, the optional set of extension words is defined as the “Operand Data.”
7.3.3.3 COMMAND SEQUENCE DIAGRAM.
7-7
) illustrates the serial bus traffic for each command. Each bubble in the diagram
represents a single 17-bit transfer across the bus. The top half in each bubble corresponds
to the data transmitted by the development system to the debug module; the bottom half
corresponds to the data returned by the debug module in response to the development
system commands. Command and result transactions are overlapped to minimize latency.
A command sequence diagram (see
Figure
The cycle in which the command is issued contains the development system command
mnemonic (in this example, “read memory location”). During the same cycle, the debug
module responds with either the lowest order results of the previous command or with a
command complete status (if no results were required).
Table 7-4. BDM Size Field Encoding
ENCODING
00
01
10
11
OPERAND SIZE
Byte
Word
Long
Reserved
F
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n
.