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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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MCP41010E/P датащи(PDF) 17 Page - Microchip Technology |
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MCP41010E/P датащи(HTML) 17 Page - Microchip Technology |
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17 / 32 page  2003 Microchip Technology Inc. DS11195C-page 17 MCP41XXX/42XXX 5.0 SERIAL INTERFACE Communications from the controller to the MCP41XXX/42XXX digital potentiometers is accom- plished using the SPI serial interface. This interface allows three commands: 1. Write a new value to the potentiometer data register(s). 2. Cause a channel to enter low power shutdown mode. 3. NOP (No Operation) command. Executing any command is accomplished by setting CS low and then clocking-in a command byte followed by a data byte into the 16-bit shift register. The com- mand is executed when CS is raised. Data is clocked- in on the rising edge of clock and out the SO pin on the falling edge of the clock (see Figure 5-1). The device will track the number of clocks (rising edges) while CS is low and will abort all commands if the number of clocks is not a multiple of 16. 5.1 Command Byte The first byte sent is always the command byte, fol- lowed by the data byte. The command byte contains two command select bits and two potentiometer select bits. Unused bits are ‘don’t care’ bits. The command select bits are summarized in Figure 5-2. The com- mand select bits C1 and C0 (bits 4:5) of the command byte determine which command will be executed. If the command bits are both 0’s or 1’s, then a NOP com- mand will be executed once all 16 bits have been loaded. This command is useful when using the daisy- chain configuration. When the command bits are 0,1, a write command will be executed with the 8 bits sent in the data byte. The data will be written to the potentiom- eter(s) determined by the potentiometer select bits. If the command bits are 1,0, then a shutdown command will be executed on the potentiometers determined by the potentiometer select bits. For the MCP42XXX devices, the potentiometer select bits P1 and P0 (bits 0:1) determine which potentiome- ters are to be acted upon by the command. A corre- sponding ‘1’ in the position signifies that the command for that potentiometer will get executed, while a ‘0’ sig- nifies that the command will not effect that potentiometer (see Figure 5-2). 5.2 Writing Data Into Data Registers When new data is written into one or more of the poten- tiometer data registers, the write command is followed by the data byte for the new value. The command select bits C1, C0 are set to 0,1. The potentiometer selection bits P1 and P0 allow new values to be written to potentiometer 0, potentiometer 1 (or both) with a sin- gle command. A ‘1’ for either P1 or P0 will cause the data to be written to the respective data register and a ‘0’ for P1 or P0 will cause no change. See Figure 5-2 for the command format summary. 5.3 Using The Shutdown Command The shutdown command allows the user to put the application circuit into a power-saving mode. In this mode, the A terminal is open-circuited and the B and W terminals are shorted together. The command select bits C1, C0 are set to 1,0. The potentiometer selection bits P1 and P0 allow each potentiometer to be shut- down independently. If either P1 or P0 are high, the respective potentiometer will enter shutdown mode. A ‘0’ for P1 or P0 will have no effect. The eight data bits following the command byte still need to be transmitted for the shutdown command, but they are ‘don’t care’ bits. See Figure 5-2 for command format summary. Once a particular potentiometer has entered the shut- down mode, it will remain in this mode until: • A new value is written to the potentiometer data register, provided that the SHDN pin is high. The device will remain in the shutdown mode until the rising edge of the CS is detected, at which time the device will come out of shutdown mode and the new value will be written to the data regis- ter(s). If the SHDN pin is low when the new value is received, the registers will still be set to the new value, but the device will remain in shutdown mode. This scenario assumes that a valid com- mand was received. If an invalid command was received, the command will be ignored and the device will remain in the shutdown mode. It is also possible to use the hardware shutdown pin and reset pin to remove a device from software shut- down. To do this, a low pulse on the chip select line must first be sent. For multiple devices, sharing a single SHDN or RESET line allows you to pick an individual device on that chain to remove from software shutdown mode. See Figure 1-3 for timing. With a preceding chip select pulse, either of these situations will also remove a device from software shutdown: • A falling edge is seen on the RS pin and held low for at least 150 ns, provided that the SHDN pin is high. If the SHDN pin is low, the registers will still be set to mid-scale, but the device will remain in shutdown mode. This condition assumes that CS is high, as bringing the RS pin low while CS is low is an invalid state and results are indeterminate. • A rising edge on the SHDN pin is seen after being low for at least 100 ns, provided that the CS pin is high. Toggling the SHDN pin low while CS is low is an invalid state and results are indeterminate. • The device is powered-down and back up. Note: The hardware SHDN pin will always put the device in shutdown regardless of whether a potentiometer has already been put in the shutdown mode using the software command. |
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