HD64F2149YV datasheet(734/1075 Pages) RENESAS

734 / 1075 page

Section 22 ROM

Rev. 3.00 Jan 18, 2006 page 706 of 1044

REJ09B0280-0300

Automatic SCI Bit Rate Adjustment

Start

bit

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

System Clock Frequency for which Automatic Adjustment

of the Chip’s Bit Rate is Possible

19200 bps

8 MHz to 10 MHz

9600 bps

4 MHz to 10 MHz

4800 bps

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

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