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MCP4641-502E/MS 数据表(PDF) 50 Page - Microchip Technology |
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MCP4641-502E/MS 数据表(HTML) 50 Page - Microchip Technology |
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50 / 92 page ![]() MCP454X/456X/464X/466X DS22107A-page 50 © 2008 Microchip Technology Inc. 6.2.4 ADDRESSING The address byte is the first byte received following the START condition from the master device. The address contains four (or more) fixed bits and (up to) three user defined hardware address bits (pins A2, A1, and A0). These 7-bits address the desired I2C device. The A7:A4 address bits are fixed to “0101” and the device appends the value of following three address pins (A2, A1, A0). Address pins that are not present on the device are pulled up (a bit value of ‘1’). Since there are up to three adress bits controlled by hardware pins, there may be up to eight MCP4XXX devices on the same I2C bus. Figure 6-9 shows the slave address byte format, which contains the seven address bits. There is also a read/ write bit. Table 6-2 shows the fixed address for device. Hardware Address Pins The hardware address bits (A2, A1, and A0) correspond to the logic level on the associated address pins. This allows up to eight devices on the bus. These pins have a weak pull-up enabled when the VDD < VBOR. The weak pull-up utilizes the “smart” pull-up technology and exhibits the same characteristics as the High-voltage tolerant I/O structure. The state of the A0 address pin is latch on POR/BOR. This is required since High Voltage commands force this pin (HVC/A0) to the VIHH level. FIGURE 6-9: Slave Address Bits in the I2C Control Byte. TABLE 6-2: DEVICE SLAVE ADDRESSES 6.2.5 SLOPE CONTROL The MCP45XX/46XX implements slope control on the SDA output. As the device transitions from HS mode to FS mode, the slope control parmameter will change from the HS specification to the FS specification. For Fast (FS) and High-Speed (HS) modes, the device has a spike suppression and a Schmidt trigger at SDA and SCL inputs. Device Address Comment MCP45X1 ‘0101 11’b + A0 Supports up to 2 devices. Note 1 MCP45X2 ‘0101 1’b + A1:A0 Supports up to 4 devices. Note 1 MCP46X1 ‘0101’b + A2:A1:A0 Supports up to 8 devices. Note 1 MCP46X2 ‘0101 1’b + A1:A0 Supports up to 4 devices. Note 1 Note 1: A0 is used for High-Voltage commands and the value is latched at POR. SA6A5 A4A3 A2 A1 A0 R/W A/A Start bit Slave Address R/W bit A bit (controlled by slave device) R/W = 0 = write R/W = 1 = read A = 0 = Slave Device Acknowledges byte A = 1 = Slave Device does not Acknowledge byte “0” “1” “0” “1” See Table 6-2 |
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