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EXTERNAL REFERENCE INPUT
ARCHIVED BY FREESCALE SEMICONDUCTOR, INC. 2005
To use an external reference, disconnect J3, J4, J13, and J14. Use a reference signal at J2 which com-
plies with data sheet requirements. Then modify the reference frequency in the program main menu to
reflect the changes made (F menu item).
DATA TRANSFER FROM COMPUTER TO EVK
To control the serial input EVK with the parallel printer port, a conversion is done. Printer cards are de-
signed to output eight bits through eight lines. A bit mask is used to obtain the bit combination for the
three required output lines (Data, Clock, Load). As bytes are sent to the printer card in sequence, it ap-
pears to be a serial transfer. The printer port is used because data transfer using the serial port would be
much slower. A standard IBM PC can support a parallel port data rate of 4.77 MHz.
IBM PCs and compatibles can accept up to three printer port configurations. These ports are called
LPT1, LPT2, and LPT3. Each printer port has a unique address. Two sets of addresses are in common
use. One set applies to IBM PC XT, AT, and clones. The other is for the PS 2 line. To load data into the
EVK, the correct address must be selected. The program default is $278. If $278 is not the address in
use, it must be modified by entering the P menu item in the main menu. All allowed addresses given in
hexadecimal are as follows:
Up to three EVK boards can operate independently from one printer port. All lines on the printer port are
connected to every EVK. Even with three boards operating, only three output lines (Clock, Data, and
Load) from the printer card are used. If two boards are controlled together, data for the second board is
received from the Output A of the first. Output A is a configurable output on '220 devices, which in this
case is used to shift data through chip 1 into chip 2. Output A and Data are connected using a printer port
input line. This was done to avoid connecting extra wires. Fortunately not all port input lines are needed
for computer input. Load and Clock are common to both boards.
A three–board cascade is handled similarly to a two–board cascade. Out A on the first board is fed to
Data on the second. Out A on the second connects to Data on the third. Instructing the program on the
quantity of boards connected together allows it to modify the number of bits sent.
All boards have a DIP switch S1 which gives each a unique address. The configuration menu is used to
tell the program what type of board is connected at a board address. Switch positions for all possible
addresses are given in Figure 3.
MOTOROLA
Freescale Semiconductor, Inc.
Label
IBM PC and Clones
LPT1
LPT2
LPT3
For More Information On This Product,
Go to: www.freescale.com
278
378
3BC
PS 2
3BC
378
278
MC145220EVK
11
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