AS3658F-BCTP datasheet(141/158 Pages) AMSCO

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Revision 1v13

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AS3658

Data Sheet Confidential - Deta il ed Descri ption - System Functi ons

10.9

Real-Time Clock (RTC) Module

The RTC module provides time information to the system. It is implemented as a 6-bit counter that is incremented

every second - with the 32kHz oscillator delivering the necessary accurate time base – and is reset to 0 each time the

counter value is 60. An additional 24-bit minute counter is incriminated each time the 6-bit counter is reset to 0. Both

counters are set to 0 at a power-on-reset. The host controller can set the counter to any value by setting the RTC 1…4

registers.

To prevent ambiguous time information because of the 30-bit value being incremented before all of the 4 registers

have been read or written, a 30-bit parallel shadow register is implemented. Every time a write/read access via the

serial interface occurs the parallel shadow register is updated with the current value of the 30-bit counter. Any write

access to the RTC 1 register will disable the update of the parallel register and set the value of the appropriate byte of

the parallel register. Any subsequent write access to the RTC 4 register will transfer the current value of the 30-bit

parallel register to the RTC 1…4 registers and the update of the parallel register is enabled again. Similarly, any read

access to the RTC 1 register will freeze the current value of the parallel register and submit the appropriate byte to the

host controller via the serial interface. Any subsequent read access to the RTC 4 register will enable the update of the

parallel register again. This mechanism makes sure that the maximum error of the value that is written to or read from

the registers is 1 second.

The startup state after power on reset:RTCSecond=3F, RTCMinute1=FF, RTCMinute2=FF, RTCMinute3=FF

To start the RTC, rtc_mode bits have to be set to a non zero value, and the RTC registers have to be set.

The RTC stops automatically at its highest value (3F,FF,FF,FF) to prevent overrun.

Table 168. RTC Second Register

Addr:64

RTCSecond

These bits represents the actual RTC second register

Bit

Bit Name

Default

Access

Description

Table 169. RTC Minute1 Register

Addr:65

RTCMinute1

These bits represents the actual RTC Minute1 register

Bit

Bit Name

Default

Access

Description

Table 170. RTC Minute2 Register

Addr:66

RTCMinute2

These bits represents the actual RTC Minute2 register

Bit

Bit Name

Default

Access

Description

Table 171. RTC Minute3 Register

Addr:67

RTCMinute3

These bits represents the actual RTC Minute3 register

Bit

Bit Name

Default

Access

Description

5:0

RTCSecond

00h

R/W

Bits 5:0 of the 6-bit RTC second counter

7:6

reserved

7:0

RTCMinute1

00h

R/W

Bits 7…0 of the 24-bit RTC minute counter

7:0

RTCMinute2

00h

R/W

Bits 15:8 of the 24-bit RTC minute counter

7:0

RTCMinute3

00h

R/W

Bits 23:16 of the 24-bit RTC minute counter

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