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Description of the Command Codes
3-8
3.5
Description of the Command Codes
3.5.1
Command Header 1—Configure Internal Registers
This command is used to configure the MSP53C691 internal registers. Certain
values in certain registers are not allowed to be modified (see note at the end
of this section). Attempting to modify these values when writing to those regis-
ters has no effect. The command header for configuring internal registers for
the MSP53C691 is one nibble long and of value 1 as shown. This header is
sent across the four data lines. The sequence of events to configure the inter-
nal registers is as follows:
1) The MSP53C691 pulls INRDY low to request a command or data.
2) The master sends the command header 0x1 over the data lines.
Write Operation to Configure Internal Registers
Data Lines
DATA4
DATA3
DATA2
DATA1
DATA0
0
0
0
0
1
3) The MSP53C691 pulls INRDY low again to request level 1 parameters.
The level 1 parameter that defines the address of the internal register is
two nibbles long in this case, see the following examples:
Most significant (first
nibble)
Least significant ( Second nibble)
X
X
4) The master sends the two nibbles back to back in response to the two
consecutive lowerings of INRDY.
Note:
When sending the two nibbles that make up the address of the register, send
the first nibble (most significant) first.
Example 1: To configure pins 7 and 5 of port D as outputs and pins 6 and 4
as inputs, we need to write to the port D control register. The address for the
register to be configured is 0x1C, then the two nibbles (8 bits) are written as
1C:
MSB
LSB
7
6
5
4
3
2
1
0
0
0
0
1
1
1
0
0
Perform the following write operation by writing the two nibbles (8 bits) MSB
first, as shown. The two nibbles are written one nibble at a time—in each case
the DATA4 bit is pulled low, indicating that a command is being sent.
Содержание MSP53C691
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