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RV5C387A Datasheet(PDF) 18 Page - RICOH electronics devices division |
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RV5C387A Datasheet(HTML) 18 Page - RICOH electronics devices division |
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18 / 42 page  RV5C387A PRELIMINARY 12345 - 18 - 14. USAGE 14.1. Interfacing with the CPU The RV5C387A employs the I 2C-Bus system to be connected to the CPU via 2-wires. Connection and system of I 2C-Bus are described in the following sections. 14.1.1. Connection of I 2C-Bus 2-wires, SCL and SDA pins that are connected to I2C-Bus are used for transmit clock pulses and data respectively. All ICs that are connected to these lines are designed that will not be clamped when a voltage beyond supply voltage is applied to input or output pins. Open drain pins are used for output. This construction allows communication of signals between ICs with different supply voltages by adding a pull-up resistor to each signal line as shown in the figure below. Each IC is designed not to affect SCL and SDA signal lines when power to each of these is turned off separately. Micro- Controller RV5C387A Other Peripheral Device VDD1 VDD2 VDD3 VDD4 SCL SDA * For data interface, the following conditions must be met: VDD4 ≥VDD1 VDD4 ≥VDD2 VDD4 ≥VDD3 * When the master is one, the micro- controller is ready for driving SCL to “H” and Rp of SCL may not be required. Rp Rp Cautions on determining Rp resistance, (1) Dropping voltage at Rp due to sum of input current or output current at off conditions on each IC pin connected to the I 2C-Bus shall be adequately small. (2) Rising time of each signal be kept short even when all capacity of the bus is driven. (3) Current consumed in I 2C-Bus is small compared to the consumption current permitted for the entire system. When all ICs connected to I 2C-Bus are CMOS type, condition (1) may usually be ignored since input current and off-state output current is extremely small for the many CMOS type ICs. Thus the maximum resistance of Rp may be determined based on (2), while the minimum on (3) in most cases. In actual cases a resistor may be place between the bus and input/output pins of each IC to improve noise margins in which case the Rp minimum value may be determined by the resistance. Consumption current in the bus to review (3) above may be expressed by the formula below: Bus consumption current ≈ (Sum of input current and off state output current of all devices in standby mode ) × Bus standby duration Bus stand-by duration + the Bus operation duration + Supply voltage × Bus operation duration × 2 Rp resistance × 2 × (Bus stand-by duration + bus operation duration) + Supply voltage × Bus capacity × Charging/Discharging times per unit time Operation of “ × 2” in the second member denominator in the above formula is derived from assumption that “L” duration of SDA and SCL pins are the half of bus operation duration. “ × 2” in the numerator of the same member is because there are two pins of SDA and SCL. The third member, (charging/discharging times per unit time) means number of transition from “H” to “L” of the signal line. |
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