LSI Symbios SYM53C040, Technical Manual

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2-18 Functional Description
2.6.4 Firmware Download and Checksum
The first step in the download is to read in the destination address and
firmware length. Then the firmware will be read in and written out starting
at the destination address. Each byte is bit wise XORed with the previous
checksum, starting with zeros. The final byte read is the checksum value.
This byte is compared to the calculated checksum. Bit 0 of the
Miscellaneous register ( 0xFD04 ) indicates a checksum error. If this bit is
high after download, there was a difference between the calculated
checksum and the last byte read in at download.
2.6.5 Manually Accessing External Two-Wire Serial Devices
The SYM53C040 Two-Wire Serial interface allows the microcontroller
core to manually access external two-wire devices such as temperature
sensors, A/D converters, memory devices or any other I/O device that
adheres to the standard Two-Wire Serial protocol. The SYM53C040 Two-
Wire Serial interface always performs single byte read and write
operations when accessed through the register interface, so it is not
intended for maximum throughput with large blocks of data.
Figure 2.11
and Figure 2.12 are flowcharts of SYM53C040 serial transmit and
receive operations.