A000047 Arduino, A000047 Datasheet - Page 251

• Manufacturer Part Number: A000047
• Description: MCU, MPU & DSP Development Tools Mega2560
• Manufacturer: Arduino
• Series: -r
• Type: MCUr

Specifications of A000047

• Processor To Be Evaluated: ATmega2560
• Interface Type: USB, I2C, SPI
• Dimensions: 4 in x 2.1 in
• Operating Supply Voltage: 5 V
• Contents: Board
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: ATmega2560

2549M–AVR–09/10
1
2
3
4
5
ldi
out
wait1:
in
sbrs r16,TWINT
rjmp wait1
in
andi r16, 0xF8
cpi
brne ERROR
ldi
out
ldi
out
wait2:
in
sbrs r16,TWINT
rjmp wait2
in
andi r16, 0xF8
cpi
brne ERROR
ldi
out
ldi
out
Assembly Code Example
r16, (1<<TWINT)|(1<<TWSTA)|
(1<<TWEN)
TWCR, r16
r16,TWCR
r16,TWSR
r16, START
r16, SLA_W
TWDR, r16
r16, (1<<TWINT) | (1<<TWEN)
TWCR, r16
r16,TWCR
r16,TWSR
r16, MT_SLA_ACK
r16, DATA
TWDR, r16
r16, (1<<TWINT) | (1<<TWEN)
TWCR, r16
Even though this example is simple, it shows the principles involved in all TWI transmissions.
These can be summarized as follows:
•
•
•
In the following an assembly and C implementation of the example is given. Note that the code
below assumes that several definitions have been made, for example by using include-files.
When the TWI has finished an operation and expects application response, the TWINT Flag
is set. The SCL line is pulled low until TWINT is cleared.
When the TWINT Flag is set, the user must update all TWI Registers with the value relevant
for the next TWI bus cycle. As an example, TWDR must be loaded with the value to be
transmitted in the next bus cycle.
After all TWI Register updates and other pending application software tasks have been
completed, TWCR is written. When writing TWCR, the TWINT bit should be set. Writing a
one to TWINT clears the flag. The TWI will then commence executing whatever operation
was specified by the TWCR setting.
TWCR = (1<<TWINT)|(1<<TWSTA)|
while (!(TWCR & (1<<TWINT)))
if ((TWSR & 0xF8) != START)
TWDR = SLA_W;
TWCR = (1<<TWINT) | (1<<TWEN);
while (!(TWCR & (1<<TWINT)))
if ((TWSR & 0xF8) !=
MT_SLA_ACK)
TWDR = DATA;
TWCR = (1<<TWINT) | (1<<TWEN);
(1<<TWEN)
;
ERROR();
;
ERROR();
ATmega640/1280/1281/2560/2561
C Example
indicates that the SLA+W has been
status different from MT_SLA_ACK
Load SLA_W into TWDR Register.
indicates that the START condition
Clear TWINT bit in TWCR to start
Clear TWINT bit in TWCR to start
status different from START go to
transmitted, and ACK/NACK has
Load DATA into TWDR Register.
Register. Mask prescaler bits. If
Register. Mask prescaler bits. If
Wait for TWINT Flag set. This
Wait for TWINT Flag set. This
Check value of TWI Status
Check value of TWI Status
transmission of address
Send START condition
has been transmitted
transmission of data
been received.
go to ERROR
Comments
ERROR
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