AS8228 datasheet(72/123 Pages) AMSCO

72 / 123 page

Data Sheet AS8218 / AS8228

Revision 3.0, 31-May-06

Page 72 of 123

Address Roll Over

When the highest address on the EEPROM is reached, e.g. 7FFFh for a 32kB device, then the address counter

must roll over to 0000h.

Unused Upper Address Bits

Unused upper address bits must be ignored in any case. E.g. an 8kB device has a maximum address of 1FFFh

must interpret 7FFFh as 1FFFh, ignoring the higher bits.

Program Length

The program length is stored at the 2 topmost locations, means for a 32kB EEPROM at 7FFEh and 7FFFh. It is

possible to use any smaller EEPROM as long as it is guaranteed that

a) the upper unused address bits are ignored

b) an address roll over is performed after the highest address

Timing of AS8218 / AS8228 Boot Sequence

Detailed SPI timing generated by the AS8218 / AS8228 – see SPI section.

Figure 13: Timing diagram

The diagram shows the sequence applied to the EEPROM after device reset.

On the EEP_SI line you see:

03h (READ)

7Fh (address high)

FEh (address low)

On the EEP_SO line you see the answer of the EEPROM. In this case the first two values 22h and 00h are

forming the program length, means 0022h = 34 bytes are to be fetched and stored to the program memory

(P_RAM). The next values are 02h, 00h, 16h (LJMP 0016h) representing the first bytes of the program code.

03h

FEh

00h

75h

22h

02h

16h

90h

7Fh

AS8228 Datasheet(PDF) 72 Page - ams AG