MPC555
/
MPC556
DEVELOPMENT SUPPORT
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
21-40
21.5.6.9 Serial Data Into Development Port
In debug mode the 35 bits of the development port shift register are interpreted as a
start/ready bit, a mode/status bit, a control/status bit, and 32 bits of data. All instruc-
tions and data for the CPU are transmitted with the mode bit cleared indicating a 32-
bit data field. The encoding of data shifted into the development port shift register
(through the DSDI pin) is shown below in
.
Data values in the last two functions other than those specified are reserved.
All transmissions from the debug port on DSDO begin with a “0” or “ready” bit. This
indicates that the CPU is trying to read an instruction or data from the port. The exter-
nal development tool must wait until it sees DSDO go low to begin sending the next
transmission.
The control bit differentiates between instructions and data and allows the develop-
ment port to detect that an instruction was entered when the CPU was expecting data
and vice versa. If this occurs a sequence error indication is shifted out in the next serial
transmission.
The trap enable function allows the development tool to transfer data to the trap enable
control register.
The debug port command function allows the development tool to either negate break-
point requests, reset the processor, activate or deactivate the fast down load proce-
dure.
The NOP function provides a null operation for use when there is data or a response
to be shifted out of the data register and the appropriate next instruction or command
will be determined by the value of the response or data shifted out.
Table 21-13 Debug Instructions / Data Shifted Into Development Port Shift Register
Start
Mode
Control
Instruction / Data (32 Bits)
Function
Bits 0:6
Bits 7:31
1
0
0
CPU Instruction
Transfer Instruction
to CPU
1
0
1
CPU Data
Transfer Data
to CPU
1
1
0
Trap enable
1
NOTES:
Not exist
Transfer data to
Trap Enable
Control Register
1
1
1
0011111
Not exist
Negate breakpoint requests
to the CPU.
1
1
1
0
Not exist
nop
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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