AN2681 Freescale Semiconductor / Motorola, AN2681 Datasheet - Page 2

• Manufacturer Part Number: AN2681
• Description: 1-Wire Interface on the i.MX21 Application Processor
• Manufacturer: Freescale Semiconductor / Motorola

Freescale Semiconductor, Inc.
Introduction
1.2 Communication Protocol
To communicate with the DS2751, the 1-Wire Interface must follow a protocol. The flowchart below,
reproduced from the DS2751 specification, illustrates the transaction flow required between the i.MX21
processor and the DS2751.
Figure 2.
DS2751 1-Wire Communication
When idle, the 1-Wire bus is high until the i.MX21 drives it low during a reset pulse. The bus is held low
for a specified time interval, subsequently the slave devices respond with a presence pulse. When the
presence of slave devices has been detected, the i.MX21 proceeds to the addressing portion of the
sequence.
As shown in Figure 2, there are four valid Net Address Commands:
1. Read: the DS2751 address, if the DS2751 is the only device connected. Otherwise, all devices try
to transmit their address, which results in a data collision.
2
MC9328MX21 Application Note
MOTOROLA
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