MC68HC912D60 Datasheet, PDF (344/432 Pages) Freescale Semiconductor, Inc – M68HC12 Microcontrollers

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Table 19-2. Hardware Commands⁽¹⁾
Command
BACKGROUND
READ_BD_BYTE⁽¹⁾
READ_BD_WORD⁽¹⁾
READ_BYTE
READ_WORD
Opcode
(Hex)
90
E4
EC
E0
E8
Data
Description
None
Enter background mode if firmware enabled.
16-bit address
16-bit data out
Read from memory with BDM in map (may steal
cycles if external access) data for odd address on
low byte, data for even address on high byte.
16-bit address Read from memory with BDM in map (may steal
16-bit data out cycles if external access). Must be aligned access.
16-bit address
16-bit data out
Read from memory with BDM out of map (may steal
cycles if external access) data for odd address on
low byte, data for even address on high byte.
16-bit address Read from memory with BDM out of map (may steal
16-bit data out cycles if external access). Must be aligned access.
WRITE_BD_BYTE⁽¹⁾
C4
16-bit address
16-bit data in
Write to memory with BDM in map (may steal cycles
if external access) data for odd address on low
byte, data for even address on high byte.
WRITE_BD_WORD⁽¹⁾
CC
16-bit address Write to memory with BDM in map (may steal cycles
16-bit data in if external access). Must be aligned access.
WRITE_BYTE
C0
16-bit address
16-bit data in
Write to memory with BDM out of map (may steal
cycles if external access) data for odd address on
low byte, data for even address on high byte.
WRITE_WORD
C8
16-bit address Write to memory with BDM out of map (may steal
16-bit data in cycles if external access). Must be aligned access.
1. Use these commands only for reading/writing to BDM locations.The BDM firmware ROM and BDM registers are not nor-
mally in the HC12 MCU memory map.Since these locations have the same addresses as some of the normal application
memory map, there needs to be a way to decide which physical locations are being accessed by the hardware BDM
commands.This gives rise to needing separate memory access commands for the BDM locations as opposed to the
normal application locations.In logic, this is accomplished by momentarily enabling the BDM memory resources, just for
the access cycles of the READ_BD and WRITE_BD commands.This logic allows the debugging system to unobtrusively
access the BDM locations even if the application program is running out of the same memory area in the normal appli-
cation memory map.
The second type of BDM commands are firmware commands
implemented in a small ROM within the HC12 MCU. The CPU must be
in background mode to execute firmware commands. The usual way to
get to background mode is by the hardware command BACKGROUND.
The BDM ROM is located at $FF20 to $FFFF while BDM is active. There
are also seven bytes of BDM registers located at $FF00 to $FF06 when
BDM is active. The CPU executes code in the BDM firmware to perform
the requested operation. The BDM firmware watches for serial
commands and executes them as they are received. The firmware
commands are shown in Table 19-3.
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68HC(9)12D60 — Rev 4.0
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