Boot Mode - Renesas H8S/2158 User Manual

Section 24 ROM
24.7.1

Boot Mode

Table 24.5 shows the boot mode operations between reset end and branching to the programming
control program.
1. When boot mode is used, 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 24.8, Flash Memory Programming/Erasing. In boot mode, if any data
exists in the flash memory (except in the case that all data are 1), all blocks in the flash
memory are erased. Use boot mode at initial writing in the on-board state, or forced recovery
when user program mode cannot be executed because the program to be initiated in user
program mode was mistakenly erased.
2. The SCI_1 should be set to asynchronous mode, and the transfer format as follows: 8-bit data,
1 stop bit, and no parity.
3. When the boot program is initiated, this LSI measures the low-level period of asynchronous
SCI communication data (H'00) transmitted continuously from the host. This LSI then
calculates the bit rate of transmission from the host, and adjusts the SCI_1 bit rate to match
that of the host. The reset should end with the RxD1 pin high. The RxD1 and TxD1 pins
should be pulled up on the board if necessary. After the reset ends, it takes approximately 100
states before this LSI is ready to measure the low-level period.
4. After matching the bit rates, this LSI 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 this LSI. 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 this LSI. 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 24.6.
5. In boot mode, a part of the on-chip RAM area is used by the boot program. Addresses
H'FF0800 to H'FF1FFF is the area to which the programming control program is transferred
from the host. Note, however, that ID codes are assigned to addresses H'FF0800 to H'FF0807.
The boot program area cannot be used until the execution state in boot mode switches to the
programming control program. Figure 24.6 shows the on-chip RAM area in boot mode.
6. Before branching to the programming control program (H'FF0808 in the RAM area), this LSI
terminates transfer operations by the SCI_1 (by clearing the RE and TE bits in SCR to 0), but
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 TxD1 pin is in high-
level output state. The contents of the CPU general registers are undefined immediately after
Rev. 3.00 Jan 25, 2006 page 728 of 872
REJ09B0286-0300