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Standard, commercially available cables may be used in most cases. Note that the EVB requires
only three of the RS-232C signals. Table 2-2 lists these signals and their pin assignments. Other
signals have been routed through the RS-232C interface chip for proper levels. Some terminal
interface programs require proper levels on all pins to function correctly.
The EVB's RS-232C connector, P1 , is wired as Data Circuit-terminating Equipment (DCE) and
employs a 9-pin subminiature D (DB-9) receptacle.
Most terminal devices — whether dumb terminals or the serial ports on host computers — are
wired as Data Terminal Equipment (DTE) and employ 9- or 25-pin subminiature D (DB-9 or
DB-25) plugs. In these cases, normal straight-through cabling is used between the EVB and the
terminal.
Adapters are readily available for connecting 9-pin cables to 25-pin terminal
connectors.
If the terminal device is wired as DCE, the RXD and TXD lines must be cross-connected, as
shown in Table 2-2. Commercial "null modem" adapter cables are available for this purpose.
EVB P1
DCE
Receptacle
2
Receive Data (RXD)
3
Transmit Data (TXD)
5
(1)
Normal (DCE-to-DTE) cable connections
(2)
Null modem (DCE-to-DCE) cable connections
Optionally, the MCU's Background Debug Mode (BDM IN W12) interface can serve as the
user interface. This setup makes the SCI port available for user applications. Additional
hardware and software are required. For more information, refer to the documentation for the
background debug development tool being used. This can be another M68EVB912B32 or a tool
such as Motorola's Serial Debug Interface (SDI).
68EVB912B32UM/D
Table 2-2. RS-232C Interface Cabling
DTE Signal
DB-9
Ground (GND)
CONFIGURATION AND SETUP
Terminal
(1)
DTE
DCE
Plug
Receptacle
DB-25
DB-9
2
2
3
3
3
2
5
7
5
(2)
DB-25
3
2
7
2-3
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