HD64F2149 Datasheet, PDF (709/1035 Pages) Renesas Technology Corp – Hitachi 16-Bit Single-Chip Microcomputer

Automatic SCI Bit Rate Adjustment
Start
bit
D0
D1
D2
D3
D4
D5
D6
D7
Stop
bit
Low period (9 bits) measured (H'00 data)
High period
(1 or more bits)
Figure 22.9 Automatic SCI Bit Rate Adjustment
When boot mode is initiated, the 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 (4800, 9600, or 19200) bps.
Table 22.8 shows typical host transfer bit rates and system clock frequencies for which automatic
adjustment of the chip’s bit rate is possible. The boot program should be executed within this
system clock range.
Table 22.8 System Clock Frequencies for which Automatic Adjustment of the Chip’s Bit
Rate is Possible
Host Bit Rate
19200 bps
9600 bps
4800 bps
System Clock Frequency for which Automatic Adjustment
of the Chip’s Bit Rate is Possible
8 MHz to 10 MHz
4 MHz to 10 MHz
2 MHz to 10 MHz
On-Chip RAM Area Divisions in Boot Mode: In boot mode, the 1920-byte area from
H'(FF)E880 to H'(FF) EFFF and the 128-byte area from H'(FF)FF00 to H'(FF)FF7F is reserved for
use by the boot program, as shown in figure 22.10. The area to which the programming control
program is transferred is H'(FF)E080 to H'(FF)E87F (2048 bytes). However, the 8-byte area from
H'(FF)E080 to H'(FF)E087 is reserved for ID codes as shown in figure 22.10. The boot program
area can be used when the programming control program transferred into the reserved area enters
the execution state. A stack area should be set up as required.
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