Datasheet

43
4337K–USB–04/08
AT89C5130A/31A-M
10. EEPROM Data Memory
10.1 Description
The 1-Kbyte on-chip EEPROM memory block is located at addresses 0000h to 03FFh of the
ERAM memory space and is selected by setting control bits in the EECON register.
A read in the EEPROM memory is done with a MOVX instruction.
A physical write in the EEPROM memory is done in two steps: write data in the column latches
and transfer of all data latches into an EEPROM memory row (programming).
The number of data written on the page may vary from 1 to 128 bytes (the page size). When pro-
gramming, only the data written in the column latch is programmed and a ninth bit is used to
obtain this feature. This provides the capability to program the whole memory by bytes, by page
or by a number of bytes in a page. Indeed, each ninth bit is set when the writing the correspond-
ing byte in a row and all these ninth bits are reset after the writing of the complete EEPROM row.
10.2 Write Data in the Column Latches
Data is written by byte to the column latches as for an external RAM memory. Out of the 11
address bits of the data pointer, the 4 MSBs are used for page selection (row) and 7 are used for
byte selection. Between two EEPROM programming sessions, all the addresses in the column
latches must stay on the same page, meaning that the 4 MSB must not be changed.
The following procedure is used to write to the column latches:
• Set bit EEE of EECON register
• Load DPTR with the address to write
• Store A register with the data to be written
• Execute a MOVX @DPTR, A
• If needed, loop the three last instructions until the end of a 128 bytes page
10.3 Programming
The EEPROM programming consists on the following actions:
• Writing one or more bytes of one page in the column latches. Normally, all bytes must belong
to the same page; if not, the first page address will be latched and the others discarded.
• Launching programming by writing the control sequence (52h followed by A2h) to the
EECON register.
• EEBUSY flag in EECON is then set by hardware to indicate that programming is in progress
and that the EEPROM segment is not available for reading.
• The end of programming is indicated by a hardware clear of the EEBUSY flag.
10.4 Read Data
The following procedure is used to read the data stored in the EEPROM memory:
• Set bit EEE of EECON register
• Stretch the MOVX to accommodate the slow access time of the column latch (Set bit M0 of
AUXR register)
• Load DPTR with the address to read
• Execute a MOVX A, @DPTR