HD6433644R datasheet(142/549 Pages) RENESAS

142 / 549 page

Section 6 ROM

Rev. 6.00 Sep 12, 2006 page 122 of 526

REJ09B0326-0600

Automatic SCI Bit Rate Adjustment: When boot mode is initiated, the H8/3644F, H8/3643F, or

H8/3642AF measures the low period of the asynchronous SCI communication data transmitted

continuously from the host (figure 6.10). The data format should be set as 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 (9 bits), 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 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 oscillation frequency (fOSC), there will be a discrepancy between the bit

rates of the host and the chip. To insure correct SCI operation, the host’s transfer bit rate should be

set to 2400, 4800, or 9600 bps*1. Table 6.10 shows typical host transfer bit rates and system clock

oscillation frequency for which automatic adjustment of the chip’s bit rate is possible. Boot mode

should be used within this system clock oscillation frequency range*2.

Notes: 1. Only use a host bit rate setting of 2400, 4800, or 9600 bps. No other bit rate setting

should be used.

2. Although the chip may also perform automatic bit rate adjustment with bit rate and

system clock oscillation frequency combinations other than those shown in table 6.10,

a degree of error will arise between the bit rates of the host and the chip, and

subsequent transfer will not be performed normally. Therefore, only a combination of

bit rate and system clock oscillation frequency within one of the ranges shown in table

6.10 can be used for boot mode execution.

Start

bit

Stop

bit

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

High period

(1 or more

bits)

Figure 6.10 Measurement of Low Period in Transmit Data from Host

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