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Section 18 ROM
Automatic SCI Bit Rate Adjustment
Start
bit
Figure 18.7 Measuring the low period of the communication data from the host
When boot mode is initiated, this LSI measures the low period of the asynchronous SCI
communication data (H'00) transmitted continuously from the host (figure 18.7). The SCI
transmit/receive format should be set as follows: 8-bit data, 1 stop bit, no parity. This LSI
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 LSI. 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 system
clock frequency of this LSI, there will be a discrepancy between the bit rates of the host and the
LSI. To ensure correct SCI operation, the host's transfer bit rate should be set to 4800 and 9600
bps *
1
.
Table 18.7 shows typical host transfer bit rates and system clock frequencies for which automatic
adjustment of this LSI bit rate is possible. The boot program should be executed within this system
clock range *
2
.
Table 18.7 System Clock Frequencies for which Automatic Adjustment of This LSI Bit
Rate is Possible
Host Bit Rate (bps)
9600
4800
Notes: 1. The host bit rate settings are 4800 and 9600bps only. Do not use any other setting.
2. This LSI may automatically adjusts the bit rate except for bit rate and system clock
combinations as shown in Table 18.7. However, the bit rate of the host and this LSI will
be different and subsequent transfers will not be carried out normally. Therefore, always
execute the boot mode within the range of the bit rate and system clock combinations
shown in Table 18.7.
Rev. 4.00 Jan 26, 2006 page 626 of 938
REJ09B0276-0400
D0
D1
D2
D3
Low period (9 bits) measured (H'00 data)
System Clock Frequency for which Automatic Adjustment
of This LSI Bit Rate is Possible (MHz)
8 to 20
4 to 20
D4
D5
D6
D7
Stop
bit
High period
(1 or more bits)
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