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MCP4142T-104E/MS 数据表(PDF) 41 Page - Microchip Technology |
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MCP4142T-104E/MS 数据表(HTML) 41 Page - Microchip Technology |
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41 / 88 page ![]() © 2008 Microchip Technology Inc. DS22059B-page 41 MCP414X/416X/424X/426X 6.1.4 SERIAL CLOCK (SCK) (SPI FREQUENCY OF OPERATION) The SPI interface is specified to operate up to 10 MHz. The actual clock rate depends on the configuration of the system and the serial command used. Table 6-1 shows the SCK frequency for different configurations. TABLE 6-1: SCK FREQUENCY 6.1.5 THE CS SIGNAL The Chip Select (CS) signal is used to select the device and frame a command sequence. To start a command, or sequence of commands, the CS signal must transition from the inactive state (VIH) to an active state (VIL or VIHH). After the CS signal has gone active, the SDO pin is driven and the clock bit counter is reset. If an error condition occurs for an SPI command, then the Command byte’s Command Error (CMDERR) bit (on the SDO pin) will be driven low (VIL). To exit the error condition, the user must take the CS pin to the VIH level. When the CS pin returns to the inactive state (VIH) the SPI module resets (including the address pointer). While the CS pin is in the inactive state (VIH), the serial interface is ignored. This allows the Host Controller to interface to other SPI devices using the same SDI, SDO, and SCK signals. The CS pin has an internal pull-up resistor. The resistor is disabled when the voltage on the CS pin is at the VIL level. This means that when the CS pin is not driven, the internal pull-up resistor will pull this signal to the VIH level. When the CS pin is driven low (VIL), the resistance becomes very large to reduce the device current consumption. The high voltage capability of the CS pin allows High Voltage commands. High Voltage commands allow the device’s WiperLock Technology and write protect features to be enabled and disabled. Memory Type Access Command Read Write, Increment, Decrement Non-Volatile Memory SDI, SDO 10 MHz 10 MHz (2, 3) SDI/SDO (1) 250 kHz (4) 10 MHz (2, 3) Volatile Memory SDI, SDO 10 MHz 10 MHz SDI/SDO (1) 250 kHz (4) 10 MHz Note 1: MCP41X1 devices only 2: Non-Volatile memory does not support the Increment or Decrement command. 3: After a Write command, the internal write cycle must complete before the next SPI command is received. 4: This is the maximum clock frequency without an external pull-up resistor. Note: There is a required delay after the CS pin goes active to the 1st edge of the SCK pin. |
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