attiny24v ATMEL Corporation, attiny24v Datasheet - Page 128

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

128
ATtiny24/44/84
Table 14-2
used for the USI Data Register and the 4-bit counter.
Table 14-2.
• Bit 1 – USICLK: Clock Strobe
Writing a one to this bit location strobes the USI Data Register to shift one step and the counter
to increment by one, provided that the software clock strobe option has been selected by writing
USICS1:0 bits to zero. The output will change immediately when the clock strobe is executed,
i.e., during the same instruction cycle. The value shifted into the USI Data Register is sampled
the previous instruction cycle.
When an external clock source is selected (USICS1 = 1), the USICLK function is changed from
a clock strobe to a Clock Select Register. Setting the USICLK bit in this case will select the
USITC strobe bit as clock source for the 4-bit counter (see
The bit will be read as zero.
• Bit 0 – USITC: Toggle Clock Port Pin
Writing a one to this bit location toggles the USCK/SCL value either from 0 to 1, or from 1 to 0.
The toggling is independent of the setting in the Data Direction Register, but if the PORT value is
to be shown on the pin the corresponding DDR pin must be set as output (to one). This feature
allows easy clock generation when implementing master devices.
When an external clock source is selected (USICS1 = 1) and the USICLK bit is set to one, writ-
ing to the USITC strobe bit will directly clock the 4-bit counter. This allows an early detection of
when the transfer is done when operating as a master device.
The bit will read as zero.
USICS1
0
0
0
1
1
1
1
shows the relationship between the USICS1:0 and USICLK setting and clock source
USICS0
Relationship between the USICS1:0 and USICLK Setting
0
0
1
0
1
0
1
USICLK
0
1
X
0
0
1
1
Clock Source
No Clock
Software clock strobe (USICLK)
Timer/Counter0 Compare Match
External, positive edge
External, negative edge
External, positive edge
External, negative edge
Table
4-bit Counter Clock Source
No Clock
Software clock strobe (USICLK)
Timer/Counter0 Compare Match
External, both edges
External, both edges
Software clock strobe (USITC)
Software clock strobe (USITC)
14-2).
8006H–AVR–10/09