Theory of Operation 4
Keysight 34420A Service Guide 125
The main CPU communicates with the earth referenced processor U700 through
an optically isolated (U506 and U704) asynchronous serial link. Data is sent in an
11-bit frame at a rate of 187.5 k bits/second. When the RS-232 interface is
selected, data is sent across the isolated link at 93.75 k bits/second. The 11-bit
data frame is configured for one start bit, eight data bits, one control bit, and one
stop bit.