DS2174

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1. GENERAL OPERATION

1.1 Pattern Generation

Polynomial Generation

The DS2174 has a tap select register that can be used as a mask to tap up to 32 bits in the feedback path

of the polynomial generator. It also features a seed register that can be used to preload the polynomial

generator with a seed value. This is done on the rising edge of TL in Control Register 1.

The DS2174 generates polynomial patterns of any length up to and including 2

standard polynomials can be programmed using the control registers. The polynomial is generated using a

shift register of programmable length and programmable feedback tap positions. The user has access to

all combinations of pattern length and pattern tap location to gene rate industry-standard polynomials or

other combinations as well. In addition, the QRSS pattern described in T1.403 is described by the

polynomial 2

whenever the next 14 bits are ZERO.” Setting the QRSS bit in Control Register 1 causes the pattern

generator to enforce this rule.

Repetitive Pattern Generation

In addition to polynomial patterns, the DS2174 generates repetitive patterns of considerable length. The

programmer has access to 512 bytes of memory for storing pattern. The pattern length bits PL0 through

PL8, located at addresses 02h and 03h, are used to program the length of the repetitive pattern. Memory is

addressed indirectly and is used to store the pattern. Data can be sent MSB or LSB first as it appears in

the memory.

Repetitive patterns can include simple patterns such as 3 in 24, but the additional memory can be used to

store patterns such as DDS-n patterns or T1-n patterns. Repetitive patterns are stored in increments of 8

bits. To generate a repetitive pattern that is 12 bits long (3 nibbles), the pattern is written twice such that

the pattern is 24 bits long (3 bytes), and repeats twice in memory. The same is true when the device is

used in serial mode: a 5-bit pattern is written to memory 5 times. For example,

To generate a 00001 pattern at the serial output, write these bytes to memory:

RAM ADDRESS

BINARY CODE

HEX CODE

00h

00010000

10h

01h

01000010

42h

02h

00001000

08h

03h

00100001

21h

04h

10000100

84h