AS8218 datasheet(92/123 Pages) AMSCO

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Data Sheet AS8218 / AS8228

Revision 3.0, 31-May-06

Page 92 of 123

Boot Loader (BOOTLOAD)

After power-up the boot loader loads the program data from the EEPROM down to the on-chip P_RAM (Note:

Parameters or settings stored in the EEPROM will not be loaded by BOOTLOAD, this will be handled by the

MCU program.).

Only when this is finished the chip can start with its normal operation. (It is also possible to trigger a bootload

during normal operation, when for example a new program has been written to the EEPROM (debugging!))

The BOOTLOAD block can be seen as a direct interface between SPI and P_RAM.

BOOTLOAD

MCU

SPI

P_RAM

boot_sel

EEPROM

AS8218/AS8228

Figure 24: BOOTLOAD block diagram

EEPROM Data Organisation

Program data are stored beginning at address 0000h.

Program data size must not be bigger than 24,576 bytes (0000h – 6000h-1), due to P_RAM size.

The length of the program must be stored at the two topmost bytes. The program length is given as number

of bytes, expressed as hexadecimal. The lower byte goes to the lower address, the higher byte to the

higher address. For a 32kB EEPROM this means: 7FFEh: Length, lower byte, 7FFFh: Length, higher byte.

If the length value is bigger than 6000h, the bootloader will just stop after 6000h program data bytes.

If the length value is 0000h or FFFFh, no program load will be done.

It is also possible to use smaller sized EEPROMs, the length value still has to be stored in the two topmost

bytes. The bootloader will always read from the two topmost 32kB addresses, which then are assumed to

‘rolled down’ to the existing two topmost addresses. This adds flexibility to the system configuration.

Meter data and system parameters (selects etc.) are stored in the remaining memory space. The allocation

of memory space is totally up to the MCU program.

Please note that the program data is not protected against overwrites from the MCU program.

Case of No Program:

In case there is no program stored in the EEPROM (boot loader detects all 0s or all 1s at the program

length address) the boot loader writes ‘SJMP $’ (Hex code: 80FEh) to address 0 of the P_RAM. This

guarantees the well defined behavior after first power on.

AS8218 датащи(PDF) 92 Page - ams AG