MCP413X/415X/423X/425X
7.1
Command Byte
7.0
DEVICE COMMANDS
The Command Byte has three fields, the Address, the
Command, and 2 Data bits, see Figure 7-1. Currently
only one of the data bits is defined (D8). This is for the
Write command.
The MCP4XXX’s SPI command format supports 16
memory address locations and four commands. Each
command has two modes. These are:
• Normal Serial Commands
The device memory is accessed when the master
sends a proper Command Byte to select the desired
operation. The memory location getting accessed is
contained in the Command Byte’s AD3:AD0 bits. The
action desired is contained in the Command Byte’s
C1:C0 bits, see Table 7-1. C1:C0 determines if the
desired memory location will be read, written,
Incremented (wiper setting +1) or Decremented (wiper
setting -1). The Increment and Decrement commands
are only valid on the volatile wiper registers.
• High-Voltage Serial Commands
Normal serial commands are those where the CS pin is
driven to VIL. High Voltage Serial Commands, CS pin is
driven to VIHH, for compatibility with systems that also
support the MCP414X/416X/424X/426X devices. High
Voltage Serial Commands operate identically to their
corresponding Normal Serial Command. In each
mode, there are four possible commands. These
commands are shown in Table 7-1.
The 8-bit commands (Increment Wiper and Decre-
ment Wiper commands) contain a Command Byte,
see Figure 7-1, while 16-bit commands (Read Data
and Write Data commands) contain a Command Byte
and a Data Byte. The Command Byte contains two data
bits, see Figure 7-1.
As the Command Byte is being loaded into the device
(on the SDI pin), the device’s SDO pin is driving. The
SDO pin will output high bits for the first six bits of that
command. On the 7th bit, the SDO pin will output the
CMDERR bit state (see Section 7.3 “Error Condi-
tion”). The 8th bit state depends on the the command
selected.
Table 7-2 shows the supported commands for each
memory location and the corresponding values on the
SDI and SDO pins.
TABLE 7-1:
COMMAND BIT OVERVIEW
Table 7-3 shows an overview of all the SPI commands
and their interaction with other device features.
C1:C0 Bit
States
Command
# of Bits
Read Data
Write Data
Increment
Decrement
16-Bits
16-Bits
8-Bits
11
00
01
10
8-Bits
16-bit Command
Data Byte
8-bit Command
Command Byte
Command Byte
A A A A C C D D D D D D D D D D
D D D D 1 0 9 8 7 6 5 4 3 2 1 0
3 2 1 0
A A A A C C D D
D D D D 1 0 9 8
3 2 1 0
Command
Bits
C C
1 0
Data
Bits
0 0 = Write Data
0 1 = INCR
1 0 = DECR
Data
Bits
Command
Bits
Memory
Address
Memory
Address
Command
Bits
1 1 = Read Data
FIGURE 7-1:
General SPI Command Formats.
© 2008 Microchip Technology Inc.
DS22060B-page 47
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