Z8F042ASJ020EG2156 Datasheet, PDF (199/280 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F082A Series
Product Specification
184
host is the character 80H. The character 80H has eight continuous bits Low (one Start bit
plus 7 data bits), framed between High bits. The Auto-Baud Detector measures this period
and sets the OCD Baud Rate Generator accordingly.
The Auto-Baud Detector/Generator is clocked by the system clock. The minimum baud
rate is the system clock frequency divided by 512. For optimal operation with asynchro-
nous datastreams, the maximum recommended baud rate is the system clock frequency
divided by 8. The maximum possible baud rate for asynchronous datastreams is the sys-
tem clock frequency divided by 4, but this theoretical maximum is possible only for low
noise designs with clean signals. Table 108 lists minimum and recommended maximum
baud rates for sample crystal frequencies.
Table 108. OCD Baud-Rate Limits
System Clock
Frequency (MHz)
20.0
1.0
0.032768 (32 kHz)
Recommended Maximum
Baud Rate (Kbps)
2500.0
125.0
4.096
Recommended
Standard PC Baud
Rate (bps)
1,843,200
115,200
2,400
Minimum Baud
Rate (Kbps)
39
1.95
0.064
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 F082A 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
PS022828-0413
PRELIMINARY
Operation