Rainbow Electronics ATmega8HVD - Manual (Page 18)

18
8052B–AVR–09/08
ATmega4HVD/8HVD
7.6.3 EECR – The EEPROM Control Register
• Bits 7:6 – Res: Reserved Bits
These bits are reserved bits in the ATmega4HVD/8HVD and will always read as zero.
• Bits 5, 4 – EEPM1 and EEPM0: EEPROM Programming Mode Bits
The EEPROM Programming mode bit setting defines which programming action that will be
triggered when writing EEPE. It is possible to program data in one atomic operation (erase the
old value and program the new value) or to split the Erase and Write operations in two differ-
ent operations. The Programming times for the different modes are shown in
Table 7-1 . While
EEPE is set, any write to EEPMn will be ignored. During reset, the EEPMn bits will be reset to
0b00 unless the EEPROM is busy programming.
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM Ready Interrupt if the I bit in SREG is set. Writing
EERIE to zero disables the interrupt. The EEPROM Ready interrupt generates a constant
interrupt when EEPE is cleared.
• Bit 2 – EEMPE: EEPROM Master Write Enable
The EEMPE bit determines whether setting EEPE to one causes the EEPROM to be written.
When EEMPE is set, setting EEPE within four clock cycles will write data to the EEPROM at
the selected address If EEMPE is zero, setting EEPE will have no effect. When EEMPE has
been written to one by software, hardware clears the bit to zero after four clock cycles. See the
description of the EEPE bit for an EEPROM write procedure.
• Bit 1 – EEPE: EEPROM Write Enable
The EEPROM Write Enable Signal EEPE is the write strobe to the EEPROM. When address
and data are correctly set up, the EEPE bit must be written to one to write the value into the
EEPROM. The EEMPE bit must be written to one before a logical one is written to EEPE, oth-
erwise no EEPROM write takes place. The following procedure should be followed when
writing the EEPROM (the order of steps 3 and 4 is not essential):
1. Wait until EEPE becomes zero.
2. Write new EEPROM address to EEARL (optional).
3. Write new EEPROM data to EEDR (optional).
Bit 7 6 5 4 3 2 1 0
– – EEPM1 EEPM0 EERIE EEMPE EEPE EERE EECR
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value 0 0 X X 0 0 X 0
Table 7-1. EEPROM Mode Bits
EEPM1 EEPM0
Typ Programming Time,
f
OSC
= 4.0 MHz Operation
0 0 3.4 ms
Erase and Write in one operation
(Atomic Operation)
0 1 1.8 ms Erase Only
1 0 1.8 ms Write Only
1 1 – Reserved for future use