Renesas H8S Series Hardware Manual page 618

16-bit single-chip microcomputer

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Automatic SCI Bit Rate Adjustment

When boot mode is initiated, the H8S/2357 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 (4,800, or 9,600) bps.

Table 19-15 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 19-15 System Clock Frequencies for which Automatic Adjustment of H8S/2357 Bit Rate is Possible

Host Bit Rate

On-Chip RAM Area Divisions in Boot Mode: In boot mode, the 2 kbytes area from H'FFDC00 to H'FFE3FF is reserved

for use by the boot program, as shown in figure 19-17. The area to which the programming control program is transferred

is H'FFE400 to H'FFFB7F. The boot program area can be used when the programming control program transferred into

RAM enters the execution state. A stack area should be set up as required.

Rev.6.00 Oct.28.2004 page 590 of 1016

REJ09B0138-0600H

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

Figure 19-16 Automatic SCI Bit Rate Adjustment

System Clock Frequency for which Automatic Adjustment

of H8S/2357 Bit Rate is Possible

(1 or more bits)