MULTI-MODE COUNTER SECTION 13
Page 13-1 RPC-320
DESCRIPTION
The 24 bit multimode counter is capable of up/down,
binary, divide-by-n, and quadrature inputs. Count
frequency is DC to 20 Mhz. The RPC-320 uses an LSI
Computer Systems LS7166. Its data sheet is found in
Appendix C.
The COUNT function and statement are used to read
from and write to the counter . LINEB is used to
program the chip for various operating modes.
An interrupt, using ONITR, may be detected on a carry,
borrow, or either event. The event is jumper selectable
through W8. When the counter is used, external
interrupts (see Chapter 12) may not be used.
W8 Pin Description
1-2 External TTL level through P2-6 or
optically isolated through P3
3-4 Carry or borrow pulse from counter
5-6 Carry pulse from counter
7-8 Borrow pulse from counter
Signals connect to the counter via P2. Use the following
table to determine signal input to the LS7166.
P2 Function
Name
A IN Count input A
B IN Count input B
GND Ground
LOAD Load counter/latch (LCTR/LLTC)
GATE Gate/reset counter (ABGT/RCTR)
Input lines (A IN), (B IN), LOAD, and GATE are
pulled to + 5V through a 10K resistor.
PROGRAMMING
The LS7166 is capable of several operating modes, all of
which are not discussed here. See Appendix C for this
chips operating modes. What are shown are examples of
how to program this chip.
NOTE: Be sure to initialize the counter chip before
using COUNT com mands. Failure to do so
returns meaningless results.
The COUNT function returns the current counter value.
Specifically, RPBASIC writes a 2 to the MCR (Master
Control Register), reads the 3 counter bytes from the OL
(Output latch), and converts it to the proper internal
BASIC format.
100 A = COUNT(0)
COUNT statement writes a 24 bit number to the PR
(Preset register) only. Its syntax is:
200 COUNT 0, D
To transfer this number to the counter, execute the
following in the program:
LINEB 6,1,8
The counter number is always 0 on the RPC-320.
LINEB is used to access specific registers within the
chip. Accessing control and status registers is shown
below. Counter bank is 6.
100 A = LINEB(6,1) : REM Read OSR
200 LINEB6,1,X
Line 200 writes to OCCR, ICR, QR, MCR, and ICR
registers. W hich register selected is determined by bits
6 and 7 in the byte written to the chip.
Program examples
This code resets the counter and enables the inputs. The
count is printed once a second. To see the count change,
momentarily bring "A IN" or "B IN" on P2 to ground.
When "B IN" is grounded, the count decrem ents.
10 LINEB6,1,32
20 LINEB6,1,64+8
30 ONTICK 1,500
40 GOTO 40
500 PRINT COUNT(0)
510 RETI
Line 20 can be shortened somewhat. 64 selects the ICR
(Input control register ) and 8 enables inputs. 72 could
have been used.
