Renesas Hitachi H8S/2194 Series Hardware Manual page 168

(1) Automatic SCI Bit Rate Adjustment
Start
bit
When boot mode is initiated, the MCU 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 MCU 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 MCU. 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 MCU. To ensure
correct SCI operation, the host's transfer bit rate should be set to (2400, 4800, or 9600) bps.
Table 7.6 shows typical host transfer bit rates and system clock frequencies for which automatic
adjustment of the MCU's bit rate is possible. The boot program should be executed within this
system clock range.
Table 7.6 System Clock Frequencies for which Automatic Adjustment of This LSI Bit
Rate is Possible
Host Bit Rate
9600 bps
4800 bps
D0 D1 D2
Low period (9 bits) measured (H'00 data)
Figure 7.9 Automatic SCI Bit Rate Adjustment
System Clock Frequency for which Automatic Adjustment
of This LSI Bit Rate is Possible
8 MHz to 10 MHz
4 MHz to 10 MHz
D3 D4 D5
Rev. 2.0, 11/00, page 141 of 1037
Stop
D6 D7
bit
High period
(1 or more bits)