Digital Voice Systems AMBE-3000 Specifications download pdf (Page 62)

AMBE-3000™ Vocoder Chip Users Manual

Version 2.8, August, 2011

Dat

a and Configuration Packets

6.4 Packet Interfaces

The AMBE-3000™ Vocoder Chip supports three separate physical interfaces that handle packets: UART, parallel port, and

McBSP serial port. The user selects one of the three ports via configuration pins which are read by the AMBE-3000™

Vocoder Chip after power-up or reset. The packet formats are identical regardless of which physical interface is selected.

Only one port is active at a time.

6.5 Packet Format

The AMBE-3000™ Vocoder Chip supports packets with a parity field or packets without a parity field. The packet format is

as shown in Table 28 General Packet Format WITHOUT Parity Field and Table 29 General Packet F

ormat WITH Parity Field .

A packet always starts with a PACKET HEADER byte. The next two bytes contain the PACKET LENGTH and the next byte

contains the PACKET TYPE. Each packet can contain one or more fields which are shown as FIELD0 through FIELDn in

Table 28 and Table 29. By default, parity fields are enabled after reset.

General Packet Format WITHOUT Parity Field

Packet Header Fields

START_BYTE LENGTH TYPE FIELD

… FIELD

N-1

1 byte 2 bytes 1 byte L

bytes … L

N-1

bytes

0x61 LLLL TT

Table 28 General Packet Format WITHOUT Parity Field

General Packet Format WITH Parity Field

Packet Header Fields Parity

START_BYTE LENGTH TYPE FIELD

… FIELD

N-1

PKT_PARITY PARITY_BYTE

1 byte 2 bytes 1 byte L

bytes … L

N-1

bytes 1 byte 1 byte

0x61 LLLL TT 0x2F PP

Table 29 General Packet Format WITH Parity Field

6.5.1 START_BYTE (1 byte)

Referring to Table 28 General Packet Format WITHOUT Parity Field, the START_BYTE byte always has a fixed value of

0x61.

6.5.2 LENGTH (2 bytes)

Referring to Table 28 General Packet Format WITHOUT Parity Field and Table 29 General Packet Format WITH Parity Field

, the PACKET LENGTH occupies the second two bytes of the packet. The MS byte of the packet length is the second byte of

e packet and the LS byte of the packet length is the third byte of the packet. To calculate the PACKET LENGTH take the

sum of L

through L

N-1

plus the parity bytes (if parity is used). Do not include the 4 bytes (START_BYTE, PACKET

LENGTH, and PACKET TYPE) from the Packet Header in the PACKET LENGTH. Therefore in Table 28 General Packet

Form

at WITHOUT Parity Field the PACKET LENGTH is the sum of L

through L

N-1

. With Parity field Enabled as shown in

Table 29 General Packet F

ormat WITH Parity Field , the PACKET LENGTH is the sum of L

through L

N-1

plus the Parity

bytes.

Note that the PACKET LENGTH excludes the first 4 bytes taken up by the START_BYTE, PACKET LENGTH, and

PACKET TYPE. PACKET LENGTH is therefore the total length (in bytes) of the entire packet minus 4 bytes.

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