Zarlink Semiconductor Inc.

Zarlink, ZL and the Zarlink Semiconductor logo are trademarks of Zarlink Semiconductor Inc.

Contents

1.0 Heading

2.0 Latching the Time of Day (ToD) seed

3.0 Tracking the Time of Day (ToD) information

1.0 Heading

Many of today's Timing applications (e.g., Wireless

basestations) require precise ToD (Time of Day)

information in addition to the frequency and phase

synchronization. The ToD information can come from

several different sources (e.g., GPS receiver or

Recovered ToP (Timing over Packet stream) that may

or may not reside directly on the Network timing card.

Typical Network synchronization PLLs have no

concept of the ToD, but it can be very useful to have

accurate, easily assessable ToD information on the

Timing Card. The ZL30142/143/342/343/347 allows

the user to load a ToD (Time of Day) seed into the

device from the ToD source, via the SPI

microprocessor interface. This ToD information is

synchronized with the incoming reference clock and

Sync pulse (i.e., 10 MHz clock and 1PPS sync forma

GPS receiver) allowing the device to provide a

continuous update of the ToD value, that is accessible

through the SPI microprocessor port. This application

note will detail the steps necessary to latch in the ToD

seed and track it.

December 2010

ZLAN-265

Applications of the ZL30142/143/342/343/347

Tracking ToD Information

Application Note

Figure 1 - Example Setup

GPS

Receiver

CPU

RefX

SyncX

ZL30142/143/342/343/347

10MHz

ToD

SPI

1PPS

ZLAN-265 Application Note

Zarlink Semiconductor Inc.

2.0 Latching the Time of Day (ToD) seed

1. Enable and Configure the ToD_up date register

a. Read the DCO_update register (page A, address 0x6C)

curRegValue = Read(page A, address 0x6C)

b. Set the enable_ToD_update bits [1:0] of the DCO_update register equal to '11'.

curRegValue = curRegValue | 0x03

Write(page A, address 0x6C, curRegValue )

c. Configure the ToD_update_config registers (page A, addresses 0c74 and 0x75)

Write(page A, address 0x74, 0x12 )

Write(page A, address 0x75, 0x7A )

d. (optional) Change the Update interval by configuring the ToD_update_interval

bits [3:0] in the Interval_Control register (page A, address 0x71)

Default ToD_update_interval bits [3:0] = '0111' = 7d

Default Update interval = (2ToD_update_interval+17)*12.5ns

= 2(7+17)*12.5ns = 209.7ms

2. Align the internal 1 Hz to external 1PPS sync pulse

a. Read the ToP_1Hz_alignment register (page A, address 0x72)

curRegValue = Read(page A, address 0x72)

b. Clear bits 2,3,4,5 of the ToP_1Hz_alignment register while preserving the other

curRegValue = curRegValue & 0xC3

c. Set the 1Hz_sync_ctrl bits [5:4] of the ToP_1Hz_alignment register equal to

'01' which will set an interrupt.

curRegValue = curRegValue | 0x10

Write(page A, address 0x72, curRegValue )

d. Wait for the interrupt to clear by monitoring the ToP_1Hz_alignment register

until bits 4 and 5 are cleared.

LOOP:

{

curRegValue = Read(0xA_72)

if ((curRegValue & 0x30) == 0) {BREAK}

else {CONTINUE}

}