Application Note

Theory of Operation

AN2104

5

To execute firmware commands, the user must have the BDM enabled

and active. See Table 2. When the BDM is active, it has control of the

CPU, which executes code out of the BDM ROM.

Table 2. BDM Firmware Commands

Command

Opcode (Hex)

Data

Description

READ_NEXT

62

16-bit data out

X = X + 2; Read next word

pointed to by X

READ_PC

63

16-bit data out Read program counter

READ_D

64

16-bit data out Read D accumulator

READ_X

65

16-bit data out Read X index register

READ_Y

66

16-bit data out Read Y index register

READ_SP

67

16-bit data out Read stack pointer

WRITE_NEXT

42

16-bit data in

X = X + 2; Write next word

pointed to by X

WRITE_PC

43

16-bit data in

Write program counter

WRITE_D

44

16-bit data in

Write D accumulator

WRITE_X

45

16-bit data in

Write X index register

WRITE_Y

46

16-bit data in

Write Y index register

WRITE_SP

47

16-bit data in

Write stack pointer

GO

08

None

Go to user program

TRACE1

10

None

Execute one user instruction

then return to BDM

TAGGO

18

None

Enable tagging and go to

user program

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