EXAR TAN-16

TAN-16
How to Generate a 1.544MHz (or 2.048MHz)
Clock Signal from an 8kHz Reference Clock
July 1998-2
The XRT8000 device can be configured to generate either a T1 (1.544MHz) or E1
(2.048MHz) rate clock signal, from a “Reference Clock signal of frequency 8kHz. The
approach that one should use to accomplish all of this is presented below.
1. To generate a 1.544MHz clock signal, from an 8kHz clock signal:
XR-T8000
8 kHz
F
IN
CLK1
1.544 MHz
CLK2
1.544 MHz
MSB
(CONFIG.)
Microcontroller Serial Interface
Figure 1. Illustration of the XRT8000 device generating a 1.544MHz
clock signal from an 8kHz Reference clock signal (Reverse/Slave Mode).
In order to configure the XRT8000 device to operate in this manner, the user must configure the chip to operate in the “Reverse/Slave” Mode. The user accomplishes this by
executing the following steps:
* Pull the MSB pin (pin 8) “low”.
This will configure the device to operate in the “Slave” Mode.
* Write the following values, into the corresponding “Configuration Registers”,
(via the Microprocessor Serial Interface) as tabulated below in Table 1.
Rev. 1.00
EXAR Corporation, 48720 Kato Road, Fremont, CA 94538 · (510) 668-7000 · FAX (510) 668-7017
TAN-16
Step
Number
Configuration
Register
Value
(to be written)
1
CR1
01101
Comments
The first four bits (e.g., “0110”) configures
the chip to operate in the “Reverse” Mode.
Further, it configures each of the PLLs to
generate a 1.544 MHz clock signal.
Setting the fifth bit to “1”, enables PLL #1.
If one does not wish to generate the
1.544 MHz clock via pin 6, then one should
set this bit to “0”.
2
CR2
00001
This step simply enables PLL #2 to
output a 1.544 MHz clock via the “CLK2”
output pin (pin 13). If one does not wish
to output any signal via this pin, then he/
she should write “00000” to this register.
3
CR3
xxxxx
This step can be skipped
4
CR4
xxxxx
This step can be skipped
5
CR5
11100
This step enables the XRT8000 to output
the 8kHz output via the SYNC output pin
(pin 2), and the PLL_1 and PLL_2 outputs
via the CLK1 (pin 6) and CLK2 (pin 13)
output pins, respectively.
Table 1. Programming Procedure, via the Microprocessor Serial Interface
By executing the above-mentioned procedure, the XRT8000 device will be configured to
operate in the “Forward/Slave” Mode, and will generate a 2.048MHz clock via the CLK1 and
CLK2 output pins, when receiving an 8kHz signal at the FIN input pin (pin 3).
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TAN-16
2. To generate a 2.048MHz clock signal, from an 8kHz clock signal:
XR-T8000
8 kHz
F IN
CLK1
2.048 MHz
CLK2
2.048 MHz
MSB
(CONFIG.)
Microcontroller Serial Interface
Figure 2. Illustration of the XRT8000 device generating a
2.048MHz clock signal from an 8 kHz Reference clock signal (Reverse/Slave Mode).
In order to configure the XRT8000 device to operate in this manner, the user must configure the chip to operate in the “Forward/Slave” Mode. This user accomplishes this by
executing the following steps:
*Pull the MSB pin (pin 8) “low”.
This will configure the device to operate in the “Slave” Mode.
*Write the following values, into the corresponding “Configuration Registers”,
(via the Microprocessor Serial Interface) as tabulated below.
Rev. 1.00
3
TAN-16
Step
Number
1
Configuration
Register
Value
(to be written)
CR1
00101
Comments
The first four bits (e.g., “0010”)
figures the chip to operate in the
“Forward” Mode. Further, it configures
each PLL to generate a “k x 64” clock
signal.
Note: The value for “k” is specified
in Step # 3.
Setting the fifth bit to “1”, enables PLL
# 1.
If one does not wish to generate the
2.048 MHz clock
via pin 6, then one should set this bit
to “0”.
2
CR2
00001
This step simply enables PLL #2 to
output a 2.048 MHz clock via the
“CLK2” output pin (pin 13).
If one does not wish to output any
signal via this pin, then he/she should
write “00000” to this register.
3
CR3
11111
This step sets the value for “k” for PLL
# 1 (see “Comments” for “Step 1”) to
32. Consequently, the XRT8000
will generate a clock signal of
2.048 MHz.
4
CR4
11111
5
CR5
11100
This step sets the value for “k” for PLL
# 2 (see “Comments” for “Step 1”) to
32.
This step enables the XRT8000 to
output the 8kH output via the SYNC
output pin (pin 2), and the PLL_1
and PLL_2 outputs via the CLK1 (pin
6) and CLK2 (pin 13) output pins,
respectively. By executing the abovementioned procedure, the XRT8000
device will be configured to operate in
the “Forward/Slave” Mode, and will
generate a 2.048 MHz clock via the
CLK1 and CLK2 output pins, when
receiving an 8 kHz signal at the FIN
input pin (pin 3).
Table 2. Programming Procedure, via the Microprocessor Serial Interface
Rev. 1.00
4
TAN-16
By executing the above-mentioned procedure, the XRT8000 device will be configured to
operate in the “Forward/Slave” Mode, and will generate a 2.048 MHz clock via the CLK1 and
CLK2 output pins, when receiving an 8 kHz signal at the FIN input pin (pin 3).
Rev. 1.00
5
TAN-16
NOTICE
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to
improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any
circuits described herein, conveys no license under any patent or other right, and makes no representation that
the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration
purposes and may vary depending upon a user’s specific application. While the information in this publication
has been carefully checked; no responsibility, however, is assumed for in accuracies.
EXAR Corporation does not recommend the use of any of its products in life support applications where the
failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to
significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless
EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has
been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately
protected under the circumstances.
Copyright 1998 EXAR Corporation
Datasheet July 1998
Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
Rev. 1.00
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