Table of Contents
Advertisement
UPI-41A 41AH 42 42AH USER'S MANUAL
ABSTRACTS
The UPI-41A 41AH 42 42AH is designed to fill a
wide variety of low to medium speed peripheral inter-
face applications where flexibility and easy implementa-
tion are important considerations The following exam-
ples illustrate some typical applications
Keyboard Encoder
Figure 6-1 illustrates a keyboard encoder configuration
using the UPI and the 8243 I O expander to scan a
128-key matrix The encoder has switch matrix scan-
ning logic N-key rollover logic ROM look-up table
FIFO character buffer and additional outputs for dis-
play functions control keys or other special functions
PORT 1 and PORTs 4 – 7 provide the interface to the
keyboard PORT 1 lines are set one at a time to select
the various key matrix rows
When a row is energized all 16 columns (i e PORTs
4 –7 inputs) are sampled to determine if any switch in
the row is closed The scanning software is code effi-
62
CHAPTER 6
APPLICATIONS
cient because the UPI instruction set includes individu-
al bit set clear operations and expander PORTs 4 – 7
can be directly addressed with single 2-byte instruc-
tions Also accumulator bits can be tested in a single
operation Scan time for 128 keys is about 10 ms Each
matrix point has a unique binary code which is used to
address ROM when a key closure is detected Page 3 of
ROM contains a look-up table with useable codes (i e
ASCII EBCDIC etc ) which correspond to each key
When a valid key closure is detected the ROM code
corresponding to that key is stored in a FIFO buffer in
data memory for transfer to the master processor To
avoid stray noise and switch bounce a key closure must
be detected on two consecutive scans before it is consid-
ered valid and loaded into the FIFO buffer The FIFO
buffer allows multiple keys to be processed as they are
depressed without regard to when they are released a
condition known as N-key rollover
The basic features of this encoder are fairly standard
and require only about 500 bytes of memory Since the
UPI is programmable and has additional memory ca-
pacity it can handle a number of other functions For
example special keys can be programmed to give an
entry on closing as well as opening Also I O lines are
Figure 6-1 Keyboard Encoder Configuration
231318 –43
Advertisement
Table of Contents
