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MCP795W22 Datasheet(PDF) 8 Page - Microchip Technology |
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MCP795W22 Datasheet(HTML) 8 Page - Microchip Technology |
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8 / 54 page  MCP795W1X/MCP795W2X DS22280C-page 8 Preliminary 2011-2012 Microchip Technology Inc. 3.0 SPI BUS OPERATION The MCP795WXX is designed to interface directly with the Serial Peripheral Interface (SPI) port of many of today’s popular microcontroller families, including Microchip’s PIC® microcontrollers. It may also interface with microcontrollers that do not have a built-in SPI port by using discrete I/O lines programmed properly in software to match the SPI protocol. The MCP795WXX contains an 8-bit instruction register. The device is accessed via the SI pin, with data being clocked in on the rising edge of SCK. The CS pin must be low for the entire operation. Table 3-1 contains a list of the possible instruction bytes and format for device operation. All instructions, addresses, and data are transferred MSb first, LSb last. Data (SI) is sampled on the first rising edge of SCK after CS goes low. TABLE 3-1: INSTRUCTION SET SUMMARY 3.1 Read Sequence The device is selected by pulling CS low. The various 8-bit read instructions are transmitted to the MCP795WXX followed by an 8-bit address. See Figure 3-1 for more details. After the correct instruction and address are sent, the data stored in the memory at the selected address is shifted out on the SO pin. Data stored in the memory at the next address can be read sequentially by continuing to provide clock pulses to the slave. The internal Address Pointer automatically increments to the next higher address after each byte of data is shifted out. When the highest address is reached, the address counter rolls over to the first valid address allowing the read cycle to be continued indefinitely. The read operation is terminated by raising the CS pin (Figure 1-1). FIGURE 3-1: EEREAD SEQUENCE Instruction Name Instruction Format Description EEREAD 0000 0011 Read data from EE memory array beginning at selected address EEWRITE 0000 0010 Write data to EE memory array beginning at selected address EEWRDI 0000 0100 Reset the write enable latch (disable write operations) EEWREN 0000 0110 Set the write enable latch (enable write operations) SRREAD 0000 0101 Read STATUS register SRWRITE 0000 0001 Write STATUS register READ 0001 0011 Read RTCC/SRAM array beginning at selected address WRITE 0001 0010 Write RTCC/SRAM data to memory array beginning at selected address UNLOCK 0001 0100 Unlock ID Locations IDWRITE 0011 0010 Write to the ID Locations IDREAD 0011 0011 Read the ID Locations CLRWDT 0100 0100 Clear Watchdog TImer CLRRAM 0101 0100 Clear RAM Location to ‘0’ SO SI SCK CS 0 23456 789 10 11 1 01 0 0 0 0 01 A7 A6 A5 A4 A1 A0 76543210 Data Out High-Impedance A3 A2 Address Byte 12 13 14 15 16 17 18 19 20 21 22 23 Instruction |
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Similar Description - MCP795W22 |
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