5. Available Opcodes
Table 5-1 outlines available opcodes for the AT21CS01/11.
Table 5-1. Opcodes used by the AT21CS01/11
Command 4-Bit Opcode Brief Description of Functionality
EEPROM Access 1010 (Ah) Read/Write the contents of the main memory array.
Security Register Access 1011 (Bh) Read/Write the contents of the Security register.
Lock Security Register 0010 (2h) Permanently lock the contents of the Security register.
ROM Zone Register
Access
0111 (7h) Inhibit further modification to a zone of the EEPROM array.
Freeze ROM Zone State 0001 (1h) Permanently lock the current state of the ROM Zone
registers.
Manufacturer ID Read 1100 (Ch) Query manufacturer and density of device.
Standard Speed Mode 1101 (Dh) Switch to Standard Speed mode operation (AT21CS01
only command, the AT21CS11 will NACK this command).
High-Speed Mode 1110 (Eh) Switch to High-Speed mode operation (AT21CS01/11
power‑on default. AT21CS11 will ACK this command).
5.1 EEPROM Access (Opcode Ah)
The opcode Ah is used to read data from and write data to the EEPROM. Refer to Read Operations for
more details about reading data from the device. For details about writing to the EEPROM, refer to Write
Operations.
5.2 Security Register Access (Opcode Bh)
The opcode Bh is used to read data from and write data to the Security register. Refer to Read
Operations in the Security Register for more details about reading data from the Security register. For
details about writing to the user-programmable portion of the Security register, refer to section Writing to
the Security Register.
5.3 Lock Security Register (Opcode 2h)
The opcode 2h is used to permanently lock the user-programmable portion of the Security register. Refer
to Locking the Security Register.
5.4 ROM Zone Register Access (Opcode 7h)
The AT21CS01/11 is partitioned into four, 256-bit zones, each of which can be independently and
permanently made read-only (ROM). The state of each zone is stored in a Configuration register which
can be read from or written to using the opcode 7h. The ROM Zone functionality is explained in greater
detail in ROM Zones.
AT21CS01/AT21CS11
© 2017 Microchip Technology Inc.
Datasheet
DS20005857A-page 20
