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SERIAL I/O
12.7 Receive Operation in UART Mode
32180 Group User's Manual (Rev.1.0)
Figure 12.7.7 Delay in Receive Timing
12.7.5 Start Bit Detection during UART Reception
The start bit is sampled synchronously with the internal BRG output. If the received signal remains low for 8
BRG output cycles after the falling edge of the start bit, the CPU recognizes that part of the received signal as
the start bit and starts latching the received data another 8 cycles after that, beginning with the LSB (first bit). If
some sampled part of the received signal is high before being determined to be the start bit, the CPU starts
hunting the falling edge of the received signal again. Because the start bit is sampled synchronously with the
internal BRG output, there is a delay equivalent to one BRG output cycle at maximum. The subsequent received
data is latched into the internal circuit with that delayed timing.
Figure 12.7.5 Start Bit Detection
Figure 12.7.6 Example of an Invalid Start Bit (Not Received)
Internal BRG output
RXD
LSB data
16 cycles
8 cycles 8 cycles
Note: • This diagram does not show detailed timing information.
Internal BRG output
RXD
8 cycles
Note: • This diagram does not show detailed timing information.
Internal RXD
Internal BRG output
RXD
Delay equivalent to one BRG output cycle at maximum
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