MCP39F511 datasheet(16/62 Pages) MICROCHIP

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MCP39F511

DS20005393B-page 16

 2015 Microchip Technology Inc.

4.2

Checksum

The checksum is generated using simple byte addition

and taking the modulus to find the remainder after

dividing the sum of the entire frame by 256. This oper-

ation is done to obtain an 8-bit checksum. All the bytes

of the frame are included in the checksum, including

the header byte and the number of bytes. If a frame

includes multiple command packets, none of the com-

mands will be issued if the frame checksum fails. In this

instance, the MCP39F511 will respond with a CSFAIL

response of 0x51.

On commands that are requesting data back from the

MCP39F511, the frame and checksum are created in

the same way, with the header byte becoming an

Acknowledge (0x06). Communication examples are

given in Section 4.5 “Example Communication

Frames and MCP39F511 Responses”

4.3

UART Settings

The default baud rate is 115. 2 kbps and can be

changed using the UART bits in the System

Configuration Register. This is only available on

system versions 0xFA14 and later. For previous

versions the baud rate is fixed at 115.2k. Note that the

baud rate is changed at system power-up, so when

changing the baud rate, a Save To Flash command

followed by a power-on cycle is required. The UART

operates in 8-bit mode, plus one start bit and one stop

bit, for a total of 10 bits per byte, as shown in

Figure 4-2.

FIGURE 4-2:

UART Transmission, N-8-1.

IDLE

START

IDLE

STOP

D0 D1

D3 D4

D5 D6 D7

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