Rainbow Electronics MAX6900 - Manual (Page 10)

MAX6900
I
2
C-Compatible RTC in a TDFN
10 ______________________________________________________________________________________
HEX REGISTER ADDRESS/DESCRIPTION
WRITE
ADDRESS/
COMMAND
BYTE
(HEX)
READ
ADDRESS/
COMMAND
BYTE
(HEX)
DESCRIPTION
POR
CONTENTS
D0 D1 RAM 8 Indeterminate
D2 D3 RAM 9 Indeterminate
D4 D5 RAM 10 Indeterminate
D6 D7 RAM 11 Indeterminate
D8 D9 RAM 12 Indeterminate
DA DB RAM 13 Indeterminate
DC DD RAM 14 Indeterminate
DE DF RAM 15 Indeterminate
E0 E1 RAM 16 Indeterminate
E2 E3 RAM 17 Indeterminate
E4 E5 RAM 18 Indeterminate
E6 E7 RAM 19 Indeterminate
E8 E9 RAM 20 Indeterminate
EA EB RAM 21 Indeterminate
EC ED RAM 22 Indeterminate
EE EF RAM 23 Indeterminate
F0 F1 RAM 24 Indeterminate
F2 F3 RAM 25 Indeterminate
F4 F5 RAM 26 Indeterminate
F6 F7 RAM 27 Indeterminate
F8 F9 RAM 28 Indeterminate
FA FB RAM 29 Indeterminate
FC FD RAM 30 Indeterminate
FE FF RAM Burst N/A
Table 2. Hex Register Address Definition (continued)
on the receiving end. The potential for errors occurs
when the seconds counter increments before all the
other registers are read out. For example, suppose a
carry of 13:59:59 to 14:00:00 occurs during Single
Read operations of the timekeeping registers. The net
data could become 14:59:59, which is erroneous real-
time data. To prevent this with Single Read operations,
read the Seconds register first (initial seconds) and
store this value for future comparison. When the
remaining timekeeping registers have been read out,
read the Seconds register again (final seconds). If the
initial seconds value is 59, check that the final seconds
value is still 59; if not, repeat the entire Single Read
process for the timekeeping registers. A comparison of the initial seconds value with the final seconds value
can indicate if there was a bus delay problem in read-
ing the timekeeping data (difference should always be
1s or less). Using a 100kHz bus speed, sequential
Single Reads take under 2.5ms to read all seven of the
timekeeping registers plus a second read of the
Seconds register.
The most accurate way to read the timekeeping regis-
ters is a Burst Read. In the Burst Read mode, the main
timekeeping registers (Seconds, Minutes, Hours, Date,
Month, Day, Year) and the Control register are read
sequentially. All of the main timekeeping registers and
the Control register must be read out as a group of
eight registers, with 8 bytes each, for proper execution