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24LC21 Datasheet(PDF) 5 Page - Microchip Technology |
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24LC21 Datasheet(HTML) 5 Page - Microchip Technology |
5 / 16 page 2003 Microchip Technology Inc. DS21160F-page 5 24LC21A 3.0 BIDIRECTIONAL MODE Before the 24LC21A can be switched into the Bidirectional mode (Figure 3-1), it must enter the Transition mode, which is done by applying a valid high-to-low transition on the Bidirectional mode Clock (SCL). As soon it enters the Transition mode, it looks for a control byte 1010 000X on the I2C™ bus, and starts to count pulses on VCLK. Any high-to-low transi- tion on the SCL line will reset the count. If it sees a pulse count of 128 on VCLK while the SCL line is idle, it will revert back to the Transmit-only mode, and transmit its contents starting with the Most Significant bit in address 00h. However, if it detects the control byte on the I2C™ bus, (Figure 3-2) it will switch to the in the Bidirectional mode. Once the device has made the transition to the Bidirectional mode, the only way to switch the device back to the Transmit-only mode is to remove power from the device. The mode transition process is shown in detail in Figure 3-3. Once the device has switched into the Bidirectional mode, the VCLK input is disregarded, with the exception that a logic high level is required to enable write capability. This mode supports a two-wire Bidirectional data transmission protocol (I2C™). In this protocol, a device that sends data on the bus is defined to be the transmitter, and a device that receives data from the bus is defined to be the receiver. The bus must be controlled by a master device that generates the Bidirectional mode Clock (SCL), controls access to the bus and generates the Start and Stop conditions, while the 24LC21A acts as the slave. Both master and slave can operate as transmitter or receiver, but the master device determines which mode is activated. In the Bidirectional mode, the 24LC21A only responds to commands for device 1010 000X. FIGURE 3-1: MODE TRANSITION WITH RECOVERY TO TRANSMIT-ONLY MODE FIGURE 3-2: SUCCESSFUL MODE TRANSITION TO BIDIRECTIONAL MODE TVHZ SCL SDA VCLK Transmit Only MODE Bidirectional Recovery to Transmit-only mode Bit8 (MSB of data in 00h) VCLK count = 1 2 3 4 127 128 Transition mode with possibility to return to Transmit-only mode Bidirectional permanently SCL SDA VCLK count = 1 2 n 0 VCLK Transmit Only mode MODE S1 0 1 0 0 00 0 ACK n < 128 |
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