ATA8741 ATMEL Corporation, ATA8741 Datasheet - Page 138

• Manufacturer Part Number: ATA8741
• Manufacturer: ATMEL Corporation

23. USI – Universal Serial Interface
23.1
23.2
138
Features
Overview
ATA8741
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The Universal Serial Interface (USI), provides the basic hardware resources needed for serial
communication. Combined with a minimum of control software, the USI allows significantly
higher transfer rates and uses less code space than solutions based on software only. Interrupts
are included to minimize the processor load.
A simplified block diagram of the USI is shown in
ment of I/O pins. CPU accessible I/O Registers, including I/O bits and I/O pins, are shown in
bold. The device-specific I/O Register and bit locations are listed in the
on page
Figure 23-1. Universal Serial Interface, Block Diagram
The 8-bit Shift Register is directly accessible via the data bus and contains the incoming and
outgoing data. The register has no buffering so the data must be read as quickly as possible to
ensure that no data is lost. The most significant bit is connected to one of two output pins
depending of the wire mode configuration. A transparent latch is inserted between the Serial
Register Output and output pin, which delays the change of data output to the opposite clock
edge of the data input sampling. The serial input is always sampled from the Data Input (DI) pin
independent of the configuration.
Two-wire Synchronous Data Transfer (Master or Slave)
Three-wire Synchronous Data Transfer (Master or Slave)
Data Received Interrupt
Wakeup from Idle Mode
In Two-wire Mode: Wake-up from All Sleep Modes, Including Power-down Mode
Two-wire Start Condition Detector with Interrupt Capability
146.
USIDR
USISR
USICR
2
4-bit Counter
3
2
1
0
3
2
1
0
D Q
LE
[1]
Figure 23-1 on page
TIM0 COMP
0
1
Two-wire Clock
Control Unit
CLOCK
HOLD
138. For the actual place-
“Register Descriptions”
DO
DI/SDA
USCK/SCL
9140B–INDCO–07/09
(Output only)
(Input/Open Drain)
(Input/Open Drain)