TWR-56F8400 User’s Manual
Page 8 of 35
To use an external crystal with the MC56F84789, zero ohm resistors R4 and R10 must be removed and
placed in the R5 and R7 positions. The desired crystal, load capacitors, and parallel resistor (if needed)
must be soldered to the board at Y1, C5, C6, and R6. (These components are not provided with the
TWR-56F8400 kit.) Following reset, reconfigure the GPIOC0 and GPIOC1 pins to the XTAL and EXTAL
functions to allow the use of an external crystal.
To use an external clock for the MC56F84789 make sure the zero ohm resistors are installed at R4 and
R10 and removed from R5 and R7. Provide a clock signal on either the Primary Tower Connector J500A
- pin B24 (the pin designated as CLOCKIN0) or on the AUX connector J502 - pin 8. Following reset,
configure the GPIOC0 pin to the CLKIN input function. In this mode the zero ohm resistor at R10 allows
the GPIOC1 pin of the MC56F84789 (pin 10) to be used as an input or output.
2.3.2
Serial I/O Source Select Headers
The TWR-56F8400 board allows the UART functions of the MC56F84789 DSC to be connected to a
serial interface at the primary Tower Connector J500A or through a USB bridge to the Host PC using the
OSBDM/OSJTAG MCU (U6). The selection of the RXD connections is done with the header at J8 as
shown in Table 1. The selection of the TXD connections is done with the header at J9 as shown in Table
2.
Table 1.
J8 – RXD Source Select Header
J8 – RXD Source Select Header
Pin #
Connected Signal
Description
1
ELEV_RXD0 at J500A pin A41
Shunt pins 1 and 2 together to connect the DSC
RXDO pin to the primary Tower Connector RXD0
pin. (This is a default position.)
2
GPIOF8/RXD0/TB1 from the 56F84789
DSC – pin 6 (RXD0 function)
3
RXD_SEL from the USB bridge
function on the OSBDM/OSJTAG
MCU.
Shunt pins 2 and 3 together to connect the DSC
RXD0 pin to the USB serial bridge function.
Shunt pin 3 and 4 together to connect the DSC
RXD1 pin to the USB serial bridge function.
4
GPIOF5/RXD1/XB_OUT5 from the
56F84789 DSC – pin 42 (RXD1
function)
5
ELEV_RXD1 at J500 pin A43
Shunt pins 4 and 5 together to connect the DSC
RXD1 pin to the primary Tower Connector RXD1
pin. (This is a default position.)
