Datasheet

194
2570N–AVR–05/11
ATmega325/3250/645/6450
21.4.3 USICR – USI Control Register
The Control Register includes interrupt enable control, wire mode setting, Clock Select setting,
and clock strobe.
• Bit 7 – USISIE: Start Condition Interrupt Enable
Setting this bit to one enables the Start Condition detector interrupt. If there is a pending inter-
rupt when the USISIE and the Global Interrupt Enable Flag is set to one, this will immediately be
executed. Refer to the USISIF bit description on page 193 for further details.
• Bit 6 – USIOIE: Counter Overflow Interrupt Enable
Setting this bit to one enables the Counter Overflow interrupt. If there is a pending interrupt when
the USIOIE and the Global Interrupt Enable Flag is set to one, this will immediately be executed.
Refer to the USIOIF bit description on page 193 for further details.
• Bit 5:4 – USIWM1:0: Wire Mode
These bits set the type of wire mode to be used. Basically only the function of the outputs are
affected by these bits. Data and clock inputs are not affected by the mode selected and will
always have the same function. The counter and Shift Register can therefore be clocked exter-
nally, and data input sampled, even when outputs are disabled. The relations between
USIWM1:0 and the USI operation is summarized in Table 21-1.
Bit 7 6 5 4 3 2 1 0
(0xB8) USISIE USIOIE USIWM1 USIWM0 USICS1 USICS0 USICLK USITC USICR
Read/Write R/W R/W R/W R/W R/W R/W W W
Initial Value 0 0 0 0 0 0 0 0