H838532H datasheet(154/508 Pages) RENESAS

154 / 508 page

Section 6 ROM

Rev. 1.00 May 30, 2008 Page 134 of 484

REJ09B0436-0100

3. When the boot program is initiated, the chip measures the low-level period of asynchronous

SCI communication data (H'00) transmitted continuously from the host. The chip then

calculates the bit rate of transmission from the host, and adjusts the SCI3 bit rate to match that

of the host. The reset should end with the RXD pin high. The RXD and TXD pins should be

pulled up on the board if necessary. After the reset is complete, it takes approximately 100

states before the chip is ready to measure the low-level period.

4. After matching the bit rates, the chip transmits one H'00 byte to the host to indicate the

completion 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 could

not be performed normally, initiate boot mode again by a reset. Depending on the host's

transfer bit rate and system clock frequency of this LSI, there will be a discrepancy between

the bit rates of the host and the chip. To operate the SCI properly, set the host's transfer bit rate

and system clock frequency of this LSI within the ranges listed in table 6.5.

5. In boot mode, a part of the on-chip RAM area is used by the boot program. The area H'F780 to

H'FEEF is the area to which the programming control program is transferred from the host.

The boot program area cannot be used until the execution state in boot mode switches to the

programming control program.

6. Before branching to the programming control program, the chip terminates transfer operations

by SCI3 (by clearing the RE and TE bits in SCR to 0), however the adjusted bit rate value

remains set in BRR. Therefore, the programming control program can still use it for transfer of

write data or verify data with the host. The TXD pin is high (PCR42 = 1, P42 = 1). The

contents of the CPU general registers are undefined immediately after branching to the

programming control program. These registers must be initialized at the beginning of the

programming control program, as the stack pointer (SP), in particular, is used implicitly in

subroutine calls, etc.

7. Boot mode can be cleared by a reset. End the reset after driving the reset pin low, waiting at

least 20 states, and then setting the TEST pin and P32 pin. Boot mode is also cleared when a

WDT overflow occurs.

8. Do not change the TEST pin and P32 pin input levels in boot mode.

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