Following scope picture (LeCroy Wavepro 950) shows a "ping" communication between a PC (500MHz) and a slave node. The PC sends the command CMD_PING16 with four bytes (CMD, ADDR_LSB, ADDR_MSB, CRC) at 115200 baud (upper trace, the slave address was 0xFFFF). The lower trace shows when the slave node enters or exits the serial interrupt. The middle trace shows the reply (CMD_ACK) from the slave.
As can be seen, it takes the slave 60us to receive a character and 95us to execute the "ping" command. The acknowlede is sent already 80us after the last command byte is received. This is much faster than a reply from a computer using TCP/IP which can take up to ms. What is also obvious is the large time jitter of the next PC command (the picture was accumulated for a couple of hours). This is due to the fact that Windows NT does not have predictable response times so you cannot rely on its timing. On the other side, the slave node running the ADuC812 at 11 MHz shows a response characteristic which is extremely reliable which is required in real time systems. Note that the quoted response time of 80us is valid for network commands. If an interrupt source is directly connected to the ADuC812, then the response time is 2us.
It is expected to improve this performance significantly by using the faster Cygnal microprocessor and switching to a higher baud rate. It is then expected to achive round-trip times for channel read commands of 200us.