Hitachi H8S/2633 Hardware Manual page 816

Automatic SCI Bit Rate Adjustment

When boot mode is initiated, the H8S/2633 Series 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/2633 Series 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/2633 Series. 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/2633

Series' system clock frequency, there will be a discrepancy between the bit rates of the host and

the H8S/2633 Series. Set the host transfer bit rate at 2,400, 4,800, 9,600 or 19,200 bps to operate

the SCI properly.

Table 22-7 shows host transfer bit rates and system clock frequencies for which automatic

adjustment of the H8S/2633 Series bit rate is possible. The boot program should be executed

within this system clock range.

Table 22-7 System Clock Frequencies for which Automatic Adjustment of H8S/2633 Series

Bit Rate is Possible

Host Bit Rate

Low period (9 bits) measured (H'00 data)

System Clock Frequency for Which Automatic Adjustment

of H8S/2633 Series Bit Rate is Possible

16 to 25 MHz

(1 or more bits)