6.2 Free protocol mode
In free protocol mode, EH-SIO works according to the command transmitted from CPU module. There are three types
of commands: initial setting, data receive, and data send.
6.2.1 Overview
Data Receiving
EH-SIO will start data receiving by the system, after initial setting is completed. The received data is divided
according to the message composition registered in the initial setting, and is stored in a receiving buffer. (In this
book, each data division is referred to as a “packet”.)
Figure 6.2 Structure of data receiving 1
When EH-SIO receives one or more packets in a receiving buffer, the indication of receiving packet in input
register will be added. If CPU module executes TRNS 9 (data read command) in this state, EH-SIO will send the
oldest packet from a receiving buffer to CPU module, and this area in receiving buffer is left as empty.
In addition, only one packet can be passed per the data read command. In order to have all packets sent to CPU
module, TRNS 9 (read command) must be performed until the receiving buffer is clear.
Figure 6.3 Structure of data receiving 2
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