Z8F082ASH020SC datasheet(170/244 Pages) ZILOG

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PS024705-0405

P R E L I M I N A R Y

On-Chip Debugger

Z8 Encore! XP® F08xA Series

Product Specification

152

If the OCD receives a Serial Break (nine or more continuous bits Low) the Auto-Baud

Detector/Generator resets. Reconfigure the Auto-Baud Detector/Generator by sending

80H

OCD Serial Errors

The On-Chip Debugger can detect any of the following error conditions on the DBG pin:

• Serial Break (a minimum of nine continuous bits Low)

• Framing Error (received Stop bit is Low)

• Transmit Collision (OCD and host simultaneous transmission detected by the OCD)

When the OCD detects one of these errors, it aborts any command currently in progress,

transmits a four character long Serial Break back to the host, and resets the Auto-Baud

Detector/Generator. A Framing Error or Transmit Collision may be caused by the host

sending a Serial Break to the OCD. Because of the open-drain nature of the interface,

returning a Serial Break break back to the host only extends the length of the Serial Break

if the host releases the Serial Break early.

The host transmits a Serial Break on the DBG pin when first connecting to the Z8 Encore!

XP® F08xA Series devices or when recovering from an error. A Serial Break from the host

resets the Auto-Baud Generator/Detector but does not reset the OCD Control register. A

Serial Break leaves the device in DEBUG mode if that is the current mode. The OCD is

held in Reset until the end of the Serial Break when the DBG pin returns High. Because of

the open-drain nature of the DBG pin, the host can send a Serial Break to the OCD even if

the OCD is transmitting a character.

Breakpoints

Execution Breakpoints are generated using the BRK instruction (opcode 00H). When the

eZ8 CPU decodes a BRK instruction, it signals the On-Chip Debugger. If Breakpoints are

enabled, the OCD enters DEBUG mode and idles the eZ8 CPU. If Breakpoints are not

enabled, the OCD ignores the BRK signal and the BRK instruction operates as an NOP

instruction.

Breakpoints in Flash Memory

The BRK instruction is opcode 00H, which corresponds to the fully programmed state of a

byte in Flash memory. To implement a Breakpoint, write 00H to the required break

address, overwriting the current instruction. To remove a Breakpoint, the corresponding

page of Flash memory must be erased and reprogrammed with the original data.

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