How are the Modem Lines for the Zynq-7000 SoC UART being routed and what values are they set to when not in use?
The TRM (UG585) states that the Modem signals for UART (CTSN, DCDN, DSRN, RIN, DTRN, RTSN) are routed through the EMIO. This is the case even when using MIO for Tx and Rx.
Per the TRM:
"The TX and RX interface can be mapped to either the EMIO interface or the MIO interface. The Modem control signals are only available through the EMIO interface."
When not in use, the Modem signals are all tied to 0 in the PL (Program Logic) side of the Zynq-7000 SoC board. Therefore, there must be a bitstream configuration on the PL in order to tie these values to 0. If there is no bitstream configuration, these signals will be floating and must be set manually to 0.
For 14.1 and 14.2 versions of the tools, the UART Modem signals can only be routed through EMIO when UART0 or UART1 Tx and Rx are also routed through EMIO. It is not possible to route TX and RX through MIO while at the same time routing the Modem signals through EMIO.
However, this issue has been resolved for 14.3. For 14.3 and newer versions of the tools, it is possible to route UART TX and RX through MIO while also routing the Modem signals through EMIO. Reference the images below for more clarification.
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