Z8F640x/Z8F480x/Z8F320x/Z8F240x/Z8F160x
Z8 Encore!®
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If the OCD receives a Serial Break (nine or more continuous bits Low) the Auto-Baud
Detector/Generator resets. The Auto-Baud Detector/Generator can then be reconfigured
by sending 80H.
OCD Serial Errors
The On-Chip Debugger can detect any of the following error conditions on the DBG pin:
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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 should transmit a Serial Break on the DBG pin when first connecting to the
Z8F640x family device 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 Z8F640x family 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.
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 00Hto the desired address, over-
writing the current instruction. To remove a Breakpoint, the corresponding page of Flash
memory must be erased and reprogrammed with the original data.
Watchpoints
The On-Chip Debugger can set one Watchpoint to cause a Debug Break. The Watchpoint
identifies a single Register File address. The Watchpoint can be set to break on reads and/
or writes of the selected Register File address. Additionally, the Watchpoint can be config-
ured to break only when a specific data value is read and/or written from the specified reg-
PS017610-0404
On-Chip Debugger
ZILOG [ ZILOG, INC. ]
