cmd6686gx manual - RTD Embedded Technologies, Inc.

Real Time Clock Control
The cpuModule is equipped with a Real Time Clock (RTC) which provides system date and time
functions, and also provides 128 non-volatile memory locations. The contents of these memory locations
are retained whenever an external backup battery is connected, whether or not system power
is connected.
You may access the RTC date, time, and memory using an index and data register at I/O addresses
70h and 71h. Address 70h is the Index register. It must be written with the number of the register to
read or write. Refer to the map below for valid choices for the index. Data is then written to or read
from the selected register by writing or reading (respectively) the data register at address 71h.
Do not change values stored in the RTC registers listed as
RESERVED in the table below. Doing so will interfere with proper
cpuModule operation.
Registers of the Real Time Clock are shown below:.
Real Time Clock Registers
Registers
(hex)
Registers
(decimal)
Number of
Bytes
Function
00h 0 1 BCD Seconds
02h 2 1 BCD Minutes
04h 4 1 BCD Hours
06h 6 1 Day of week
07h 7 1 Day of month
08h 8 1 Month
09h 9 1 Year
0A-31h 10-49 40 RESERVED- Do not modify!
32h 50 1 BCD Century
33-3Fh 51-63 13 RESERVED - Do not modify!
40-7Fh 64-127 64 User RAM
RTC access is illustrated in the following QuickBasic program fragment:
input "Enter address to write:", i%
input "Enter value to write:", j%
output &h70, i%
output &h71, j%
output &h70,i%
j% = input (&h71)
print "Read back value ";i%;" at address ";j%
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