DS21458 datasheet(49/270 Pages) DALLAS

49 / 270 page

DS21455/DS21458 Quad T1/E1/J1 Transceivers

49 of 270

8.1 Power-Up Sequence

The DS21455/DS21458 contain an on-chip power-up reset function, which automatically clears the

writeable register space immediately after power is supplied to the device. The user can issue a chip reset

at any time. Issuing a reset will disrupt traffic until the device is reprogrammed. The reset can be issued

through hardware using the TSTRST pin or through software using the SFTRST function in the master

mode register. The LIRST (LIC2.6) should be toggled from zero to one to reset the line interface

circuitry. (It will take the DS21455/DS21458 about 40ms to recover from the LIRST bit being toggled.)

Finally, after the TSYSCLK and RSYSCLK inputs are stable, the receive and transmit elastic stores

should be reset (this step can be skipped if the elastic stores are disabled).

8.1.1 Master Mode Register

MSTRREG

Master Mode Register

00h

Bit #

Name

—

TEST1

TEST0

T1/E1

SFTRST

Default

Bit 0/Software Issued Reset (SFTRST).

A 0 to 1 transition causes the register space to be cleared. A reset clears all configuration and status registers. The bit

automatically clears itself when the reset has completed.

Bit 1/Operating Mode (T1/E1).

Used to select the operating mode of the framer/formatter (digital) portion of the DS21455. The operating mode of the LIU

must also be programmed.

0 = T1 operation

1 = E1 operation

Bits 2, 3/Test Mode Bits (TEST0, TEST1).

Test modes are used to force the output pins of the DS21455 into known states. This can facilitate the checkout of assemblies

during the manufacturing process and also be used to isolate devices from shared buses.

TEST1

TEST0

EFFECT ON OUTPUT PINS

Operate normally

Force all output pins into tri-state (including all I/O pins and parallel port pins)

Force all output pins low (including all I/O pins except parallel port pins)

Force all output pins high (including all I/O pins except parallel port pins)

Bits 4–7/Unused, must be set to zero for proper operation.

DS21458 Datasheet(PDF) 49 Page - Dallas Semiconductor

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