ATMEGA169 ATMEL [ATMEL Corporation], ATMEGA169 Datasheet - Page 187

• Manufacturer Part Number: ATMEGA169
• Description: 8-bit Microcontroller with 16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

USI Control Register – USICR
2514P–AVR–07/06
The 4-bit counter increments by one for each clock generated either by the external
clock edge detector, by a Timer/Counter0 Compare Match, or by software using USI-
CLK or USITC strobe bits. The clock source depends of the setting of the USICS1..0
bits. For external clock operation a special feature is added that allows the clock to be
generated by writing to the USITC strobe bit. This feature is enabled by write a one to
the USICLK bit while setting an external clock source (USICS1 = 1).
Note that even when no wire mode is selected (USIWM1..0 = 0) the external clock input
(USCK/SCL) are can still be used by the counter.
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
interrupt 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 186 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 inter-
rupt 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 186 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 externally, and data input sampled, even when outputs are
disabled. The relations between USIWM1..0 and the USI operation is summarized in
Table 83.
Bit
Read/Write
Initial Value
USISIE
R/W
7
0
USIOIE
R/W
6
0
USIWM1
R/W
5
0
USIWM0
R/W
4
0
USICS1
R/W
3
0
USICS0
R/W
2
0
ATmega169/V
USICLK
W
1
0
USITC
W
0
0
USICR
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