Renesas H8S/2319 series Hardware Manual page 664

Automatic SCI Bit Rate Adjustment: When boot mode is initiated, the H8S/2319 F-ZTAT chip
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 chip 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 chip. 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 chip's system clock frequency, there will be a discrepancy between
the bit rates of the host and the chip. To ensure correct SCI operation, the host's transfer bit rate
should be set to 9,600 or 19,200 bps.
Table 17-31 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.
Start
bit
Table 17-31 System Clock Frequencies for which Automatic Adjustment of H8S/2319
F-ZTAT Bit Rate is Possible
Host Bit Rate
19,200 bps
9,600 bps
Rev. 5.00, 12/03, page 634 of 1088
D0 D1 D2
Low period (9 bits) measured (H'00 data)
Figure 17-42 Automatic SCI Bit Rate Adjustment
System Clock Frequency for which Automatic Adjustment
of H8S/2319 F-ZTAT Bit Rate is Possible
16 MHz to 25 MHz
8 MHz to 25 MHz
D3 D4 D5
Stop
D6 D7
bit
High period
(1 or more bits)