Background Debug Mode (BDM)

At the completion of cycle 3, the debug module initiates a memory read operation. Any serial transfers that begin during a memory access return a not-ready response.

Results are returned in the two serial transfer cycles after the memory access completes. For any command performing a byte-sized memory read operation, the upper 8 bits of the response data are undefined and the referenced data is returned in the lower 8 bits. The next command’s opcode is sent to the debug module during the final transfer. If a memory or register access is terminated with a bus error, the error status (S = 1, DATA = 0x0001) is returned instead of result data.

29.5.3.3 Command Set Descriptions

The following sections describe the commands summarized in Table 29-17.

NOTE:

The BDM status bit (S) is 0 for normally completed commands; S = 1 for illegal commands, not-ready responses, and transfers with bus-errors. Section 29.5.2, “BDM Serial Interface,” describes the receive packet format.

Motorola reserves unassigned command opcodes for future expansion. Unused command formats in any revision level perform a NOP and return an illegal command response.

29.5.3.3.1 Read A/D Register (RAREG/RDREG)

Read the selected address or data register and return the 32-bit result. A bus error response is returned if the CPU core is not halted.

Command/Result Formats:

15

12

11

8

7

4

3

2

0

Command

0x2

 

0x1

 

0x8

A/D

 

Register

 

 

 

 

 

 

 

 

 

Result

 

 

D[31:16]

 

 

 

 

D[15:0]

Figure 29-17. RAREG/RDREG Command Format

Command Sequence:

RAREG/RDREG

???

XXX

NEXT CMD

MS RESULT

 

 

LS RESULT

XXX

NEXT CMD

BERR

 

 

’NOT READY’

 

 

Figure 29-18. RAREG/RDREG Command Sequence

Operand Data:

None

Result Data:

The contents of the selected register are returned as a longword

 

value, most-significant word first.

MOTOROLA

Chapter 29. Debug Support

29-23

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Image 695
Motorola MCF5281, MCF5282 user manual Command Set Descriptions, Read A/D Register RAREG/RDREG, Command Sequence