Motorola MS4404 用户手册

SSI Interface

8 - 3

ACK/NAK handshaking may be enabled or disabled. If this parameter is set, all packeted messages must have a 
CMD_ACK or CMD_NAK response, unless the command description states otherwise. This parameter is enabled 
by default. This handshaking should remain enabled to provide feedback to the host. Raw decode data and 
WAKEUP do not use ACK/NAK handshaking since they are not packeted data.

Example of a problem which may occur when ACK/NAK handshaking is disabled:

The host sends a PARAM_SEND message to the decoder to change baud rate from 9600 to 19200.

The decoder cannot interpret the message. 

The decoder does not implement the changes requested by the host. 

The host assumes that the parameter changes have occurred and acts accordingly.

Communications are lost because the change did not occur on both sides.

If the ACK/NAK handshaking is enabled, the following occurs:

The host sends a PARAM_SEND message.

The decoder cannot interpret the message.

The decoder CMD_NAKs the message.

The host resends the message.

The decoder receives the message successfully, responds with CMD_ACK, and implements parameter 
changes.

The Decode Data Packet Format parameter controls how decode data is sent to the host. When this parameter is 
set, the data is sent in a DECODE_DATA packet. When the parameter is cleared, the data is transmitted as raw 
ASCII data.

When decode data is transmitted as raw ASCII data, then ACK/NAK handshaking does not apply 
regardless of the state of the ACK/NAK handshaking parameter.