Z8F1680SH020SG Datasheet, PDF (324/412 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F1680 Series
Product Specification
299
Table 162. OCD Baud-Rate Limits
System Clock
Frequency
20.0 MHz
1.0 MHz
32 kHz
Maximum Asynchronous
Baud Rate (bits/s)
2.5 M
125 k
4096
Minimum Baud
Rate (bits/s)
39.1 k
1.96K
64
If the OCD receives a Serial Break (ten or more continuous bits Low), the Autobaud
Detector/Generator resets. The Autobaud Detector/Generator can then be reconfigured by
sending 80H. If the Autobaud Detector overflows while measuring the Autobaud charac-
ter, the Autobaud Detector will remain reset.
23.2.4. High Speed Synchronous
It is possible to operate the serial On-Chip Debugger at high speeds. To operate at high
speeds, data must be synchronized with an external clock. High speed synchronous com-
munication will only work when using an external clock source. To operate in high-speed
synchronous mode, simply Autobaud to the appropriate speed. The Autobaud generator
will automatically run at the appropriate baud rate.
Slow bus rise times due to the pullup resistor become a limiting factor when operating at
high speeds. To compensate for slow rise times, the output driver can be configured to
drive the line High. If the TXD (Transmit Drive) bit is set, the line will be driven both
High and Low during transmission. The line starts being driven at the beginning of the
start bit and stops being driven at the middle of the stop bit. If the TXDH (Transmit Drive
High) bit is set, the line will be driven High until the input is High or the center of the bit
occurs, whichever is first. If both TXD and TXDH are set, the pin will be driven High for
one clock period at the beginning of each 0 to 1 transition. An example of a high-speed
synchronous interface is displayed in Figure 60.
PS025015-1212
PRELIMINARY
On-Chip Debugger