
541
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 15-11 Automatic SCI Bit Rate Adjustment
When boot mode is initiated, the H8S/2214 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 H8S/2214 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 H8S/2214. 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 H8S/2214’s system clock
frequency, there will be a discrepancy between the bit rates of the host and the H8S/2214. Set the
host transfer bit rate at 4800, 9600, or 19,200 bps to operate the SCI properly.
Table 15-9 shows host transfer bit rates and system clock frequencies for which automatic
adjustment of the H8S/2214 bit rate is possible. The boot program should be executed within this
system clock range.
Table 15-9 System Clock Frequencies for which Automatic Adjustment of H8S/2214 Bit
Rate is Possible
Host Bit Rate
System Clock Frequency for Which Automatic Adjustment
of LSI Bit Rate is Possible
4,800 bps
2 MHz to 16 MHz
9,600 bps
4 MHz to 16 MHz
19,200 bps
8 MHz to 16 MHz