Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 33)

AN93
Rev. 1.3 33
2.6.2. Three-Wire SPI Interface to EEPROM
To enable the 3-wire SPI interface to EEPROM on the 24-pin TSSOP package, appropriate pins must be reset
strapped according to Table 6 on page 14, or Table 8 on page 15, depending on the interface selected. The
EEPROM option is not available on the 24-pin TSSOP package if the parallel host interface is selected.
Figure 12 shows the connection diagram for the 3-wire SPI interface to EEPROM. A four-wire EEPROM (with
separate serial input and output data wires) may also be used with the input and output pins connected to EESD, if
its SO output is tristated on the last falling edge of EECLK during a read cycle.
Figure 12. Three-Wire EEPROM Connection Diagram
2.6.3. Detailed EEPROM Examples
Upon powerup, if the option is selected, the ISOmodem attempts to detect an EEPROM. The modem looks for a
carriage return in the first 10 memory locations. If none is found, the modem assumes the EEPROM is not
programmed and stops reading it. If a programmed EEPROM is detected, customer defaults that are programmed
into the EEPROM between the optional heading "BOOT" and the "<CR><CR>" delimiter are executed immediately,
and AT command macros are loaded into the ISOmodem RAM. The memory that may be allocated to the
<commands> portion of the EEPROM is limited to 1000 bytes. Three <CR> must be the last three entries in the
EEPROM.
EEPROM Data are stored and read in hexadecimal ASCII format in eight address blocks beginning at a specified
hexadecimal address. For example, the AT:M0000,y0,y1,y2,y3,y4,y5,y6,y7 command writes the hexadecimal
values y0…y7 at addresses from 0 to 7, respectively. The AT:E0000 command reads the hexadecimal values
y0…y7 from addresses 0 to 7, respectively.
The following sections give specific examples of EEPROM usage for command macros, firmware upgrades, boot
commands, etc.
2.6.4. Boot Commands (Custom Defaults)
Commands to be executed upon boot-up are stored between the heading BOOT and the first <CR><CR> delimiter.
The boot command has the following format:
BOOT<CR>
<commands><CR>
<commands><CR>
<CR>
HOST
SPI EEPROM
SI/SO CS SCLK
MODEM
EESD EECS SCLK
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