Z8F0830HH020SG Datasheet, PDF (161/257 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore!^® F0830 Series
Product Specification
143
If the OCD receives a serial break (nine or more continuous bits low), the autobaud detec-
tor/generator resets. Reconfigure the autobaud detector/generator by sending 80H.
OCD Serial Errors
The OCD 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 (simultaneous transmission by OCD and host 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 autobaud detec-
tor/generator. A framing error or transmit collision may be caused by the host sending a
serial break to the OCD. As a result of the open-drain nature of the interface, returning a
serial 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!
F0830 Series devices or when recovering from an error. A serial break from the host resets
the autobaud 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 OCD. 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.
PS025113-1212
Operation