Z8F021ASH020SC datasheet(196/276 Pages) ZILOG

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PS022815-0206

On-Chip Debugger

Z8 Encore! XP® 4K Series

Product Specification

177

• Step Instruction (10H)—The Step Instruction command steps one assembly instruction

at the current Program Counter (PC) location. If the device is not in DEBUG mode or the

Flash Read Protect Option bit is enabled, the OCD ignores this command.

DBG

← 10H

• Stuff Instruction (11H)—The Stuff Instruction command steps one assembly instruction

and allows specification of the first byte of the instruction. The remaining 0-4 bytes of the

instruction are read from Program Memory. This command is useful for stepping over in-

structions where the first byte of the instruction has been overwritten by a Breakpoint. If

the device is not in DEBUG mode or the Flash Read Protect Option bit is enabled, the

OCD ignores this command.

DBG

← 11H

DBG

← opcode[7:0]

• Execute Instruction (12H)—The Execute Instruction command allows sending an en-

tire instruction to be executed to the eZ8 CPU. This command can also step over Break-

points. The number of bytes to send for the instruction depends on the opcode. If the device

is not in DEBUG mode or the Flash Read Protect Option bit is enabled, this command

reads and discards one byte.

DBG

← 12H

DBG

← 1-5 byte opcode

On-Chip Debugger Control Register Definitions

OCD Control Register

The OCD Control register controls the state of the On-Chip Debugger. This register is

used to enter or exit DEBUG mode and to enable the BRK instruction. It can also reset the

Z8 Encore! XP® 4K Series device.

A reset and stop function can be achieved by writing 81H to this register. A reset and go

function can be achieved by writing 41H to this register. If the device is in DEBUG mode,

a run function can be implemented by writing 40H to this register.

DBGMODE—Debug Mode

The device enters DEBUG mode when this bit is 1. When in DEBUG mode, the eZ8 CPU

Table 109. OCD Control Register (OCDCTL)

BITS

FIELD

DBGMODE BRKEN

DBGACK

Reserved

RST

RESET

000

R/W

RRR

R/W

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