Silicon Laboratories SI2494/39 manual Three-Wire SPI Interface to Eeprom, Detailed Eeprom Examples

AN93

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.

SPI EEPROM

SI/SO CS SCLK

EESD EECS SCLK

HOST

MODEM

TELEPHONE LINE

Si3018/10

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>

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