NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
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Revision V1.30
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RS-485 Normal Multidrop Operation Mode (NMM)
In RS-485 Normal Multi-drop operation mode, software must decide whether receiver will ignore data
before an address byte is detected (bit 9 = “1”).
If software wants to receive any data before address byte detected, the flow is disable
RX_DIS(UA_FCR [8]) then enable RS485_NMM(UA_ALT_CSR[8]) and the receiver will received any
data. If an address byte is detected (bit9 =1), it will generator an interrupt to CPU and software can
decide whether enable or disable receiver to accept the following data byte by setting RX_DIS.
When an address byte be detected (bit 9 = “1”) by hardware, the address byte data will be stored in
the RX-FIFO. If the receiver is be enabled (RX_DIS(UA_FCR[8]) is low, all received byte data will be
accepted and stored in the RX-FIFO, and if the receiver is disabled (RX_DIS(UA_FCR[8]) is high, all
received byte data will be ignore until the next address byte be detected.
If software disable receiver by setting (RX_DIS(UA_FCR[8]) bit, when a next address byte be
detected, the controller will clear the RX_DIS bit and the address byte data will be stored in the RX-
FIFO.
Program Sequence Example:
1. Program FUN_SEL(UA_FUN_SEL[2:0]) to select RS-485 function.
2. Program the RX_DIS(UA_FCR[8]) bit to determine whether to store the received data before an
address byte is detected (bit 9 = “1”).
3. Program the RS485_NMM by setting RS485_NMM(UA_ALT_CSR[8]).
4. When an address byte is detected (bit 9 = “1”), hardware will set RLS_IS(UA_ISR[2]) and
RS485_ADD_DETF(UA_FSR[3]) flag.
5. Software can decide whether to accept the following data byte by setting RX_DIS(UA_FCR[8]).
6. Repeat step 4 and step 5.