LSI Symbios SYM53C040, Technical Manual

Page: 33 / 214

Two-Wire Serial Interface Operation 2-17
Figure 2.10 Serial ROM Download
On a power-on reset or on a soft-chip reset (watchdog timer expires or
the RESET/ pin toggles), the download logic will download data
beginning at address 0x00 of the two-wire slave ROM device.
2.6.3 Address and Length Download Configuration
The first four bytes read from the two-wire external ROM contain the
download destination address and the number of bytes to be
downloaded. The first byte is the destination address low byte. The
second byte is the destination address high byte. The third byte is the
firmware length low byte, and the fourth byte is the firmware length high
byte. The firmware length is the number of bytes of code not including
the two bytes of destination address, or the two bytes of firmware length.
The length does include the final checksum byte. The minimum firmware
length is three bytes.
R/W
Bit
Address High Byte
Register 0xFD05
Master
Slave S
ta
rt
C
on
di
ti
on
ACK
Re
pea
te
d
S
ta
rt
Co
nd
it
io
n
1
ACK ACK
(More data
bytes may be
transferred,
each followed
by an ACK)
S
top
C
o
n
d
it
ion
No
ACK
Data Byte Last Data Byte
RAH[7:0]
Register 0xFD00 Register 0xFD00
ACK
Address Low Byte
Register 0xFD06
RAL[7:0] Device ID 0
1 0 1 0 a b c
EEPROM
Device ID Chip
Addr
ACK
D[7:0] D[7:0]
Table 2.1 Initial ROM Download Contents
Byte Contents
0 Destination address low
1 Destination address high
2 Firmware length (n) low (includes checksum byte but not destination address bytes)
3 Firmware length (n) high
4 through n + 2 Firmware
n + 3 Checksum for firmware (up to maximum supported ROM size)