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14.3.27. Use SCC UART with Hardware Handshake

Question:
I am using a SCC port of a MPC8xx / MPC82xx as UART; for the Linux UART driver I have configured support for hardware handshake. Then I used a null-modem cable to connect the port to the serial port of my PC. But this does not work. What am I doing wrong?

Answer:
There is absolutely no way to connect a MPC8xx / MPC82xx SCC port to any DTE and use RS-232 standard hardware flow control.

Explanation:
The serial interface of the SCC ports in MPC8xx / MPC82xx processors is designed as a DTE circuitry and the RS-232 standard hardware flow control can not be used in the DTE to DTE connection with the null-modem cable (with crossed RTS/CTS signals).

The RS-232 standard specifies a DTE to DCE connection and its hardware handshaking is designed for this specific task. The hardware flow control signals in the PC (and similar equipment) are implemented as software readable/writable bits in a control register and therefore may be arbitrary treated. Unlike that, in the 8xx/82xx the handshake protocol is handled by the CPM microcode. The meaning of the signals is fixed for the RS-232 standard with no way for user to change it.

In widely spread DTE-to-DTE connections over the so called 'null-modem' cable with the hardware flow control lines the meaning of the handshake signals is changed with respect to the RS-232 standard. Therefore this approach may not be used with the 8xx/82xx.

Conclusions:
If you want to use a 8xx/82xx equipment in combination with RS-232 hardware control protocol, you must have a DCE device (modem, plotter, printer, etc) on the other end.
14.3.26. Configure Linux for XIP (Execution In Place) 1. Abstract 14.3.28. How can I access U-Boot environment variables in Linux?
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