Remote Processing RPC-220 - Manual (Page 27)

REAL TIME CLOCK SECTION 7
Page 7-2
without having to reprogram the flash every time. One
potential downside is CPU I/O ports (and registers) are
changed after a reset. R unning a program through
interr upts does not ac count for a reset.
IDLE
This mode uses more pow er (about 10 ma) but lets you
wake up on an interrupt and continue execution.
Essentially, this is the same as interrupt mode described
under "RTC INTERRUPTS" below.
INTERRUPTS
The RTC is can generate an interrupt due to several
conditions. These are described on page 7 of the
DS1689-93.PD F file. Three of the conditions (kick
start, RAM clear, and wake up) are effectively disabled
on the RPC-220. This leaves you with periodic, alarm
(specific date and time), and update interr upts.
Two of the interrupts, periodic and alarm, are described
in application programs RTC -1.C and RTC-2. C in the
RTC subdirector y. To use the interrupts, jumper J3[23-
25]. This brings the interrupt from the clock to CPU
interrupt INT1.
The RTC can generate periodic interrupts every month,
day, hour, minute, and second. It can also generate an
interrupt on a specific day, hour, minute, and/ or second
by simply progr amming the a ppropriate alar m register s.
Another periodic interrupt, using the square wave
output, is describe d next.
SQUARE WAVE OUTPUT
The RTC can output a square wave at J3-4. Frequency
ranges from 2 H z to 32.768Khz. Maximum useful sink
current is 25 ma while source current is 10 ma.
Square wave output can be used to as another clock
interrupt. T o enable, set jumper J3[4-6]. This puts the
periodic interrupt to CPU INT0. Make sure you ar e not
using INT0 on expansion port J2.
This output can also be used to trigger periodic A-D
conversions. The analog input must be enabled for
external triggers. Jumper J1[16] to J3[4] to do this. See
d e m o p r o gr a m A IN 2 2 0- 3 . C .
You can get a square wave output at J3-4 in the monitor
m o de u si ng th e M P c o mm a nd . S im p ly e nt er 0 x3 1 at I/ O
address 0xA00A and 0x8f at address 0xA00B. Square
wave output at J3-4 is 256 Hz. To change the
freque ncy, refer to Table 2 in th e DS168 9-93. PDF file
for the proper value to write to RS0-RS3.