UPD77533 datasheet(40/104 Pages) RENESAS

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Data Sheet S15671EJ4V0DS

µµµµPD77533

12.1 Packet Format

The packet format is shown below. The maximum packet length is 258 bytes.

Figure 12-1. Packet Format

12.1.1 CMD-ID field

The CMD-ID field indicates the type of command: local, extension, or server.

In the case of local commands, the CMD-ID value indicates the actual command identifier.

Table 12-1. Types of CMD-ID

CMD-ID

Type

0x00 to 0x7E

Local command (CMD-ID value indicates command identifier)

0x7F

Extension command

0x80

Server command

12.1.2 LENGTH field

The LENGTH field indicates the number of bytes in the DATA field. A value in the range of 0 to 255 is specified.

The length does not include CMD-ID, LENGTH, and FLAG.

12.1.3 DATA field

The DATA field stores the data and status of the command specified by CMD-ID.

The length of the DATA field is indicated by the value in the LENGTH field. Some commands do not include a

DATA field.

When the host CPU packets the server command, if the total length of the server command in an unpacketed

state exceeds 255 bytes, the data is divided into multiple packets.

If the size of one data item is 2 or more bytes, the data is stored in the order of lower byte(s) then higher byte(s)

(little endian).

12.1.4 FLAG field

The FLAG field contains a flag indicating the end of a packet. There are two types of flags.

Table 12-2. Flag Types

Flag

Meaning

0x03

Single packet or the last of a number of divided packets.

0x02

First packet of a number of divided packets or one of the middle packets.

1 byte

CMD-ID

FLAG

LENGTH

DATA

1 byte

Variable length (0 to 255 bytes)

Number of bytes indicated by LENGTH

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