GE B90 Instruction Manual page 79

CHAPTER 3: INSTALLATION DIRECT INPUT AND OUTPUT COMMUNICATIONS
addition, the send timing outputs of data module 1 are also paralleled to the terminal timing inputs of data module 2. By
using this configuration, the timing for both data modules and both UR RS422 channels are derived from a single clock
source. As a result, data sampling for both of the UR RS422 channels is synchronized via the send timing leads on data
module 1, shown as follows. If the terminal timing feature is not available or this type of connection is not wanted, the
G.703 interface is a viable option that does not impose timing restrictions.
Figure 3-43: Timing configuration for RS422 two-channel, three-terminal application
3
Data module 1 provides timing to the B90 RS422 interface via the ST(A) and ST(B) outputs. Data module 1 also provides
timing to data module 2 TT(A) and TT(B) inputs via the ST(A) and AT(B) outputs. The data module pin numbers have been
omitted in the figure because they vary by manufacturer.
3.4.5.3 Transmit timing
The RS422 interface accepts one clock input for transmit timing. It is important that the rising edge of the 64 kHz transmit
timing clock of the multiplexer interface is sampling the data in the center of the transmit data window. Therefore, it is
important to confirm clock and data transitions to ensure proper system operation. For example, the following figure
shows the positive edge of the Tx clock in the center of the Tx data bit.
B90 LOW IMPEDANCE BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 3-39