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3D7503 |
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MONOLITHIC MANCHESTER |
data |
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® |
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3 |
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ENCODER/DECODER |
delay |
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(SERIES 3D7503) |
devices, inc. |
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FEATURES
∙All-silicon, low-power CMOS technology
∙Encoder and decoder function independently
∙Encoder has buffered clock output
∙TTL/CMOS compatible inputs and outputs
∙Vapor phase, IR and wave solderable
∙Auto-insertable (DIP pkg.)
∙Low ground bounce noise
∙Maximum data rate: 50 MBaud
∙Data rate range: ±15%
∙Lock-in time: 1 bit
PACKAGES
CIN |
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1 |
14 |
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VDD |
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CEN |
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2 |
13 |
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CBUF |
RX |
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3 |
12 |
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LOOP |
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COUT |
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4 |
11 |
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TXENB |
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DIN |
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5 |
10 |
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DOUTB |
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RESB |
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6 |
9 |
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TXB |
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GND |
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7 |
8 |
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TX |
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3D7503-xxx |
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DIP (.300) |
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3D7503G-xxx |
Gull Wing (.300) |
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3D7503D-xxx |
SOIC (.150) |
FUNCTIONAL DESCRIPTION
The 3D7503 is a monolithic CMOS Manchester Encoder/Decoder combo chip. The device uses bi-phase-level encoding to embed a clock signal into a data stream for transmission across a communications link. In this encoding mode, a logic one is represented by a high-to-low transition in the center of the bit cell, while a logic zero is represented by a low-to-high transition.
The Manchester encoder combines the clock (CIN) and data (DIN) into a single bi-phase-level signal (TX). An inverted version of this signal (TXB) is also available. The data baud rate (in MBaud) is equal to the input clock frequency (in MHz). A replica of the clock input is also available (CBUF).
The encoder may be reset by setting the RESB input low; otherwise, it should be left high. The TX and TXB signals may be disabled (high-Z) by setting TXENB high. Similarly, CBUF may be disabled by setting CEN low. Under most operating conditions, the encoder is never reset, TX and TXB are always enabled, and CBUF is not used. With this in mind, the 3D7503 provides an internal pull-up resistor on RESB and internal pull-
down resistors on CEN and TXENB, so that most users can leave these inputs uncommitted.
The Manchester decoder accepts the embedded-clock signal at the RX input. The recovered clock and data signals are presented on COUT and DOUTB, respectively, with the data signal inverted. The operating baud rate (in MBaud) is specified by the dash number of the device. The input baud rate may vary by as much as ±15% from the nominal device baud rate without compromising the integrity of the information received.
Because the decoder is not PLL-based, it does not require a long preamble in order to lock onto the received signal. Rather, the device requires at most one bit cell before the data presented at the output is valid. This is extremely useful in cases where the information arrives in bursts and the input is otherwise turned off.
Normally, the encoder and decoder function independently. However, if the LOOP input is set high, the encoded TX signal is fed back internally into the decoder and the RX input is ignored. This feature is useful for diagnostics. The LOOP input has an internal pull-down resistor and may be left uncommitted if
this feature is not needed. |
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©1998 Data Delay Devices |
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Doc #98009 |
DATA DELAY DEVICES, INC. |
1 |
12/11/98 |
3 Mt. Prospect Ave. Clifton, NJ 07013 |
3D7503
TABLE 1: PART NUMBER SPECIFICATIONS
PART |
DECODER BAUD RATE (MBaud) |
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NUMBER |
Nominal |
Minimum |
Maximum |
3D7503-5 |
5.00 |
4.25 |
5.75 |
3D7503-10 |
10.00 |
8.50 |
11.50 |
3D7503-20 |
20.00 |
17.00 |
23.00 |
3D7503-25 |
25.00 |
21.25 |
28.75 |
3D7503-30 |
30.00 |
25.50 |
34.50 |
3D7503-40 |
40.00 |
34.00 |
46.00 |
3D7503-50 |
50.00 |
42.50 |
57.50 |
NOTE: Any baud rate between 5 and 50 MBaud not shown is also available at no extra cost.
APPLICATION NOTES
ENCODER
The Manchester encoder subsystem samples the data input at the rising edge of the input clock. The sampled data is used in conjunction with the clock rising and falling edges to generate the byphase level Manchester code.
The encoder employs the timing of the clock rising and falling edges (duty cycle) to implement the required coding scheme, as shown in Figure 1. To reduce the difference between the output data high time and low time, it is essential that the deviation of the input clock duty cycle from 50/50 be minimized.
The encoder presents at its outputs the true and the complimented encoded data. The High-to- Low time skew of the selected data output should be budgeted by the user, as it relates to his application, to satisfactorily estimate the distortion of the transmitted data stream. Such an estimate is very useful in determining the functionality and margins of the data link, if a Manchester decoder is used to decode the received data.
RESET |
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(Left high for normal operation) |
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(RESB) |
1/fC |
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1 |
0 |
1 |
1 |
0 |
0 |
1 |
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CLOCK (CIN)
tDS tDH
DATA (DIN)
T2H T2L
TRANSMIT (TXB)
T1H T1L
TRANSMIT (TX)
1 |
0 |
1 |
1 |
0 |
0 |
1 |
0 |
Figure 1: Timing Diagram (Encoder)
Doc #98009 |
DATA DELAY DEVICES, INC. |
2 |
12/11/98 |
Tel: 973-773-2299 Fax: 973-773-9672 http://www.datadelay.com |