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MCP3008T Datasheet(PDF) 19 Page - Microchip Technology |
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MCP3008T Datasheet(HTML) 19 Page - Microchip Technology |
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19 / 40 page  © 2008 Microchip Technology Inc. DS21295D-page 19 MCP3004/3008 5.0 SERIAL COMMUNICATION Communication with the MCP3004/3008 devices is accomplished using a standard SPI-compatible serial interface. Initiating communication with either device is done by bringing the CS line low (see Figure 5-1). If the device was powered up with the CS pin low, it must be brought high and back low to initiate communication. The first clock received with CS low and DIN high will constitute a start bit. The SGL/DIFF bit follows the start bit and will determine if the conversion will be done using single-ended or differential input mode. The next three bits (D0, D1 and D2) are used to select the input channel configuration. Table 5-1 and Table 5-2 show the configuration bits for the MCP3004 and MCP3008, respectively. The device will begin to sample the analog input on the fourth rising edge of the clock after the start bit has been received. The sample period will end on the falling edge of the fifth clock following the start bit. Once the D0 bit is input, one more clock is required to complete the sample and hold period (DIN is a “don’t care” for this clock). On the falling edge of the next clock, the device will output a low null bit. The next 10 clocks will output the result of the conversion with MSB first, as shown in Figure 5-1. Data is always output from the device on the falling edge of the clock. If all 10 data bits have been transmitted and the device continues to receive clocks while the CS is held low, the device will output the conversion result LSB first, as is shown in Figure 5-2. If more clocks are provided to the device while CS is still low (after the LSB first data has been transmitted), the device will clock out zeros indefinitely. If necessary, it is possible to bring CS low and clock in leading zeros on the DIN line before the start bit. This is often done when dealing with microcontroller-based SPI ports that must send 8 bits at a time. Refer to Section 6.1 “Using the MCP3004/3008 with Micro- controller (MCU) SPI Ports” , “Using the MCP3004/ 3008 with Microcontroller (MCU) SPI Ports”, for more details on using the MCP3004/3008 devices with hardware SPI ports. TABLE 5-1: CONFIGURE BITS FOR THE MCP3004 TABLE 5-2: CONFIGURE BITS FOR THE MCP3008 Control Bit Selections Input Configuration Channel Selection Single/ Diff D2* D1 D0 1 X 0 0 single-ended CH0 1 X 0 1 single-ended CH1 1 X 1 0 single-ended CH2 1 X 1 1 single-ended CH3 0 X 0 0 differential CH0 = IN+ CH1 = IN- 0 X 0 1 differential CH0 = IN- CH1 = IN+ 0 X 1 0 differential CH2 = IN+ CH3 = IN- 0 X 1 1 differential CH2 = IN- CH3 = IN+ * D2 is “don’t care” for MCP3004 Control Bit Selections Input Configuration Channel Selection Single /Diff D2 D1 D0 1 0 0 0 single-ended CH0 1 0 0 1 single-ended CH1 1 0 1 0 single-ended CH2 1 0 1 1 single-ended CH3 1 1 0 0 single-ended CH4 1 1 0 1 single-ended CH5 1 1 1 0 single-ended CH6 1 1 1 1 single-ended CH7 0 0 0 0 differential CH0 = IN+ CH1 = IN- 0 0 0 1 differential CH0 = IN- CH1 = IN+ 0 0 1 0 differential CH2 = IN+ CH3 = IN- 0 0 1 1 differential CH2 = IN- CH3 = IN+ 0 1 0 0 differential CH4 = IN+ CH5 = IN- 0 1 0 1 differential CH4 = IN- CH5 = IN+ 0 1 1 0 differential CH6 = IN+ CH7 = IN- 0 1 1 1 differential CH6 = IN- CH7 = IN+ |
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