Motorola M68HC11EVBU User Manual page 36

HARDWARE PREPARATION AND INSTALLATION
A Hayes compatible modem cable, purchased from your local computer store, can be used to
connect the EVBU to your host computer.
The EVBU is wired as data communication equipment (DCE) whereas a dumb terminal and most
serial modem ports on host computers are wired as data terminal equipment (DTE). This should
allow a straight-through cable to be used in most setups.
If an unknown cable is used to connect the EVBU to a host computer, a null modem adapter
(shown below) may be required to match the cable to the EVBU terminal port connector.
A null modem adapter is used to reverse the roles of various data and control signals to make a
DTE device appear as a DCE device or vice versa.
DB-25S
GND 1
2
TXD
RXD 3
RTS 4
CTS 5
DSR 6
SIG-GND 7
DCD 8
DTR 20
2-24
NULL MODEM ADAPTER
DB-25P
1 GND
2 TXD
3 RXD
4 RTS
CTS
5
6 DSR
7 SIG-GND
8 DCD
20
DTR
M68HC11EVBU/D