SP522 datasheet(10/23 Pages) SIPEX

10 / 23 page

Rev. 7/10/03

SP522 Multi–Mode Serial Transceivers

Unused driver inputs can be left floating; pull–

up resistors to +5V is internally connected on

the inputs so that the output is at a logic low

("0"). For differential drivers, the non-inverting

output will be at a logic high ("1").

Receivers

The SP522 has two (2) independent receivers

which can be programmed for the different

interface modes. Control for the mode selection

is done by DP0 and DP1.

Like the drivers, the receivers are pre-arranged

for the specific requirements of the interface. As

the operating mode of the receivers is changed,

the electrical characteristics will change to

support the required interface. Figures 10 to 13

show the mode of each receiver in the different

interface modes that can be selected.

There are three basic types of receiver circuits

— RS-232, RS-423, and RS-485.

The RS-232 receiver is a single–ended input

with a threshold of 0.8V to 3.0V. The RS-232

receiver has an operating voltage range of +15V

and can receive signals up to 120Kbps. The

input sensitivity complies with EIA-RS-232 and

V.28 at +3V to -3V. The input impedance is

Ω to 7kΩ.

The RS-423 receivers are also single–ended but

have an input threshold as low as +300mV. The

input impedance is guaranteed to be greater than

Ω, with an operating voltage range of +7V.

The RS-423 receivers can operate up to 120Kbps.

RS423 receivers can be used in RS-449, EIA530,

EIA-530A and V.36 applications as Category II

signals as indicated by their corresponding

specifications.

The third type of receiver is a differential which

supports RS-485. The RS-485 receiver has an

input impedance of 15K

Ω and a differential

threshold of +300mV. Since the characteristics

of an RS-422 (V.11) receiver are actually

subsets of RS-485, the receivers for RS-422

requirements are covered by the RS-485 receivers.

RS-422 receivers are used in applications for

RS-449, EIA530, EIA-530A and V.36 as

Category I signals for receiving clock, data, and

some control line signals. The differential

receivers can receive data up to 10Mbps.

All receivers include a fail-safe feature that

output a known logic state when the receiver

inputs are unconnected. For single-ended

RS-232 receivers, there are internal 5k

Ω pull-

down resistors on the inputs which produces a

logic high ("1") at the receiver outputs. The

single-ended RS-423 receivers produce a logic

low ("0") on the output when the inputs are

open. This is due to a pull-up device connected

to the input. The differential receivers have the

same internal pull-up device on the non-inverting

input which produces a logic high ("1") at the

receiver output.

The receivers also have enable pins which allow

for convenient half-duplex configurations. The

receivers are tri-stated when the ENR1 and

ENR2 pins are at a logic high ("1"). For the

SP524, ENR3 and ENR4 are used for the

additional two receivers.

In addition to the separate enable lines on each

transceiver, there is a latch enable pin,

LATCH_EN, which is used for enabling and

disabling the decoder control inputs (DP0, DP1)

and transceiver enable pins.

This pin will

default to a logic high ("1") if not being used.

Loopback

The SP522 and SP524 contain a loopback fea-

ture that allows the driver outputs to "loopback"

to the receiver inputs for diagnostic testing in

the application.

The loopback function is

activated when the LOOPBCK pin is low. When

in loopback mode, the driver outputs are

tri-stated and the receiver inputs are deactivated.

The receiver input impedance while in loopback

will be a minimum of 12k

Ω. The loopback

function can be initiated during any mode of

operation, RS-232, RS-423 or RS-422. The

travel path of the transceivers in loopback is

shown on Figure 9. The loopback function

overrides the separate enable pins for the drivers

or receivers. When LOOPBCK is at a logic low

("0"), the device will be configured in loopback

regardless whether the transceiver is enabled or

disabled.

If the loopback function is not

required, the LOOPBCK pin will default to a

logic high ("1") state.

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