Rev. 1.0, 09/02, page 456 of 568
19.6.1 Boot
Mode
Table 19.4 shows the boot mode operations from a reset end to a branch to the programming
control program.
1. In boot mode, the flash memory programming control program must be prepared in the host
beforehand. Prepare a programming control program in accordance with the description in
section 19.8, Flash Memory Programming/Erasing.
2. SCI_2 should be set to asynchronous mode with the transfer format of 8-bit data, 1 stop bit,
and no parity.
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 SCI_2 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. When the bit rate matching is completed, the chip transmits 1-byte data H
′
00 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 1-byte data H
′
55 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 19.5.
5. In boot mode, a part of the on-chip RAM area is used by the boot program. The area
H
′
FFE800 to H
′
FFEFBF is used to store the programming control program to be transferred
from the host. The boot program area cannot be used until the execution is shifted to the
programming control program.
6. Before branching to the programming control program, the chip terminates transfer operations
by SCI_2 (by clearing the RE and TE bits in SCR to 0), however the adjusted bit rate value is
retained in BRR. Therefore, the programming control program can still use it for transfer of
write data or verify data with the host. At this time, the TxD pin is in the high level output
state. 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, since 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 by driving the reset pin low, waiting at least
20 states, and then setting the mode (MD) pins. Boot mode is also cleared when a WDT
overflow occurs.
8.
Do not change the MD pin input level in boot mode.
9.
All interrupts are disabled during programming or erasing of the flash memory.
Содержание H8S/2627
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