pca8802 NXP Semiconductors, pca8802 Datasheet - Page 17

• Manufacturer Part Number: pca8802
• Description: Smartcard Rtc; Ultra Low Power Oscillator With Integrated Counter For Initiating One Time Password Generation
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCA8802_1
Product data sheet
Fig 25. Read bit order
MSB
b
23
9.6.8 Instruction rd_cmd
b
22
b
21
This instruction takes only 3 parameters in one command. Data after the 3rd parameter
will be interpreted as the next instruction.
Accurate setting and start-up can be implemented using the dvs_cmd instruction in
cooperation with the set_cmd instruction. An example is shown in
Table 8.
With the read instruction (rd_cmd) the counter value can be read at any time. When the
counter value is read, the counter is frozen so that there will be no changes during the
read back. After a read is terminated, the counter will be allowed to increment again. Any
increment that was scheduled during the frozen period will then be effected.
Reading the counter is cyclic i.e. the device will repeatedly return the present counter
value until the read is terminated. Reading the counter more than once may be useful in
the case that the application is subject to a strong Electromagnetic Interference (EMI)
environment so that read back values can be compared.
Read back must be terminated within 32 seconds else a count will be dropped.
Step
1
2
3
4
5
6
7
8
9
10
b
20
b
19
Action
initiate transfer
send wrt_cmd
enable dvs_cmd
set counter with set_cmd
end transfer
wait for an external time
marker
initiate transfer
send wrt_cmd
disable dvs_cmd
end transfer
b
18
Example of accurate setting of the counter
b
17
b
16
b
15
Rev. 01 — 19 February 2009
b
14
b
13
b
12
b
11
Code sequence Note
START condition -
1010 0000
0001 0001
1000 0000
0000 0000
0000 0000
0000 0001
STOP condition
-
START condition -
1010 0000
0001 0000
STOP condition
b
10
b
9
b
8
b
7
b
-
-
set the counter = 1
P1[23:16]
P2[15:8]
P3[7:0]
-
-
-
counter starts on the ACK cycle of this
instruction
-
6
b
5
b
4
b
3
Table
b
2
PCA8802
b
001aaj208
© NXP B.V. 2009. All rights reserved.
1
8.
Smartcard RTC
LSB
b
0
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