Renesas ZTAT H8S/2357F, Hardware Manual

Page: 663 / 1047

Rev.6.00 Oct.28.2004 page 635 of 1016
REJ09B0138-0600H
Automatic SCI Bit Rate Adjustment: When boot mode is initiated, H8S/2398 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 19-36 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
Stop
bit
D0 D1 D2 D3 D4 D5 D6 D7
Low period (9 bits) measured (H'00 data) High period
(1 or more bits)
Figure 19-45 Automatic SCI Bit Rate Adjustment
Table 19-36 System Clock Frequencies for which Automatic Adjustment of H8S/2398
F-ZTAT Bit Rate is Possible
Host Bit Rate
System Clock Frequency for which Automatic Adjustment
of H8S/2398 F-ZTAT Bit Rate Is Possible
19,200 bps 16 to 20 MHz
9,600 bps 10 to 20 MHz