Rev. 1.0, 02/00, page 143 of 1141
Automatic SCI Bit Rate Adjustment
Start
bit
Stop
bit
D0
D1
D2
D3
D4
D5
D6
D7
Low period (9 bits) measured (H'00 data)
High period
(1 or more bits)
Figure 7.9 Automatic SCI Bit Rate Adjustment
When boot mode is initiated, the LSI measures the low period of the asynchronous SCI
communication data (H'00) transmitted continuously from the host. The SCI transmit/receive
format should be set as follows: 8-bit data, 1 stop bit, no parity. The LSI calculates the bit rate of
the transmission from the host from the measured low period, and transmits one H'00 byte to the
host to indicate the end of bit rate adjustment. The host should confirm that this adjustment end
indication (H'00) has been received normally, and transmit one H'55 byte to the LSI. If reception
cannot be performed normally, initiate boot mode again (reset), and repeat the above operations.
Depending on the host's transmission bit rate and the MCU's system clock frequency, there will be
a discrepancy between the bit rates of the host and the LSI. To ensure correct SCI operation, the
host's transfer bit rate should be set to (2400, 4800, or 9600) bps.
Table 7.5 shows typical host transfer bit rates and system clock frequencies for which automatic
adjustment of the LSI’s bit rate is possible. The boot program should be executed within this
system clock range.
Table 7.5
System Clock Frequencies for which Automatic Adjustment of This LSI Bit
Rate Is Possible
Host Bit Rate (bps)
System Clock Frequency
9600
8 MHz to 10 MHz (T.B.D.)
4800
4 MHz to 10 MHz (T.B.D.)
2400
2 MHz to 10 MHz (T.B.D.)