attiny24v ATMEL Corporation, attiny24v Datasheet - Page 126

• Manufacturer Part Number: attiny24v
• Description: 8-bit Avr Microcontroller With 2/4/8k Bytes Insystem Programmable Flash
• Manufacturer: ATMEL Corporation

14.5.4
126
ATtiny24/44/84
USICR – USI Control Register
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 USICLK or USITC strobe
bits. The clock source depends on 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 choosing an external clock source
(USICS1 = 1) and writing a one to the USICLK bit.
Note that even when no wire mode is selected (USIWM1..0 = 0) the external clock input
(USCK/SCL) can still be used by the counter.
The USI Control Register includes bits for interrupt enable, setting the wire mode, selecting the
clock 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
and USISIE and the Global Interrupt Enable Flag are set to one the interrupt will be executed
immediately. Refer to the USISIF bit description on
• Bit 6 – USIOIE: Counter Overflow Interrupt Enable
Setting this bit to one enables the counter overflow interrupt. If there is a pending interrupt and
USIOIE and the Global Interrupt Enable Flag are set to one the interrupt will be executed imme-
diately. Refer to the USIOIF bit description on
• Bit 5:4 – USIWM1:0: Wire Mode
These bits set the type of wire mode to be used, as shown in
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 USI
Data Register can therefore be clocked externally and data input sampled, even when outputs
are disabled.
Bit
0x0D (0x2D)
Read/Write
Initial Value
7
USISIE
R/W
0
6
USIOIE
R/W
0
5
USIWM1
R/W
0
4
USIWM0
R/W
0
page 125
page 125
3
USICS1
R/W
0
for further details.
Table 14-1 on page
for further details.
2
USICS0
R/W
0
1
USICLK
W
0
0
USITC
W
0
127.
8006H–AVR–10/09
USICR