PCF2123 Datasheet, PDF (35/54 Pages) NXP Semiconductors – SPI Real time clock/calendar

NXP Semiconductors
PCF2123
SPI Real time clock/calendar
Table 42. Command byte definition
Bit Symbol
Value
Description
7
R/W
data read or data write selection
0
write data
1
read data
6 to 4 SA
001
subaddress; other codes will cause the device to ignore
data transfer
3 to 0 RA
0h to Fh register address range
In Figure 24, the register Seconds is set to 45 seconds and the register Minutes is set to
10 minutes.
R/W
addr 02_HEX
seconds data 45_BCD
minutes data 10_BCD
b7 b6 b5 b4 b3 b2 b1 b0 b7 b6 b5 b4 b3 b2 b1 b0 b7 b6 b5 b4 b3 b2 b1 b0
000100100100010100010000
SCL
SDI
CE
address
counter
xx
02
Fig 24. Serial bus write example
03
04
001aaf915
In Figure 25, the Months and Years registers are read. In this example, pins SDI and SDO
are not connected together. For this configuration, it is important that pin SDI is never left
floating. It must always be driven either HIGH or LOW. If pin SDI is left open, high I_DD
currents may result. Short transition periods in the order of 200 ns will not cause any
problems.
PCF2123_1
Product data sheet
Rev. 01 — 19 November 2008
© NXP B.V. 2008. All rights reserved.
35 of 54