Serial Data Wire-Wrap Connection (J23) - Motorola M68MPFB1632 User Manual

4.2.4 Serial Data Wire-Wrap Connection (J23)

The MEVB lets you define your own MCU to RS-232 interface via wire-wrap connector J23 by
providing a flexible approach to implementing an MCU-to-RS-232 interface. It lets you select
which RS-232 signals are used and to which MCU port pins they are assigned. The RS-232
circuitry, as shipped, interfaces directly with an RS-232C compatible device by connecting only
the MCU's RXD and TXD pins to J23. For pin assignments and signal descriptions of this
connector, refer to Chapter 7.
Jumper header J23 is the digital interface from the MCU to the RS-232 ports, J21 and J22.
Digital MCU signals connected to jumper header J23 pass through the level translators, U15 and
U16. These level translators provide three RS-232 drivers and receivers for each RS-232 port on
the MPFB and convert the digital signals to RS-232 voltage levels. The typical voltage levels for
RS-232 signals are +12 and -12 volts, but the voltage levels on the MEVB, via the level
translators, are +8 to -10 volts. These voltages can be seen on J21 and J22.
Figure 4-5 and 4-6 indicate the type of MCU pin (input or output) to be connected to the wire
wrap pins of J23. J23 pins 1-4, typically are connected to the MCU RXD and MCU TXD pins.
While J23 pins 5-12 provide an interface to the common RS-232 control signals. Since J23 is
user configured, you may choose to connect J23 to a UART device placed in the wire wrap area
or generate a software UART within the MCU.
Figure 4-5 describes the signal flow and connections for each RS-232 port when configured as a
DCE port via W20 or W23. Conversely Figure 4-6 describes a DTE port configuration. Both
Figure 4-5 and 4-6 indicate the signal flow, driver or receiver, for each signal with an arrow. You
should exercise caution when connecting signals to J21, J22, and J23. If you connect two drivers
together, you may damage you system or the level translators (U15 and U16) on the MPFB1632.
The RS-232 standard defines each signal with a name, i.e., RXD
but the signal flow (input or output) is determined by the port
definition, DCE or DTE. This implies that RS-232 RXD can be an
output pin. When you interface the MCU to J23, the MCU's RXD
pin is always serial data input.
M68MPFB1632/D
RS-232 I/O PORT CONFIGURATION
NOTE
4-8