SP502 datasheet(13/30 Pages) SIPEX

13 / 30 page

Rev. 7/21/03

SP502 Multi-Mode Serial Transceiver

the electrical characteristics will change to sup-

port the requirements of clock, data, and control

line receivers. Table 2 shows a summary of the

electrical characteristics of the receivers in the

different interface modes. Unused receiver in-

puts can be left floating without causing oscilla-

tion. To ensure a desired state of the receiver

output, a pull–up resistor of 100k

Ω to +5V

should be connected to the inverting input for a

logic LOW, or the non–inverting input for a

logic high. For single-ended receivers, a pull–

down resistor to ground of 5k

Ω is internally

connected, which will ensure a logic HIGH

output.

There are three basic types of receivers —

RS-232, RS-423, and RS-485. The RS-232

receiver is a single–ended input with a threshold

of 0.8V to 2.4V. The RS-232 receiver has an

operating voltage range of

±15V and can re-

ceive signals up to 120kbps. RS-232 receivers

are used in RS-232 mode for all signal types,

and in V.35 mode for control line signals.

The RS-423 receivers are also single–ended but

have an input threshold as low as

±200mV. 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.

RS-423 receivers are used for the IC signal in

RS-449 and EIA-530 modes, as shown in Table 2.

The third type of receiver supports RS-485,

which is a differential interface mode. The

RS-485 receiver has an input impedance of

15k

Ω and a differential threshold of ±200mV.

Since the characteristics of an RS-422 receiver

are actually subsets of RS-485, the receivers for

RS-422 requirements are identical to the

RS-485 receivers. RS-422 receivers are used in

RS-449 and EIA-530 for receiving clock, data,

and some control line signals. The RS-485

receivers are also used for the V.35 mode. V.35

levels require the

±0.55V signals with a load of

100

Ω. In order to meet the V.35 input imped-

ance of 100

Ω, the external termination network

of Figure 6 must be applied. The threshold of the

V.35 receiver is

±200mV. The V.35 receivers

can operate up to 5Mbps. All of the differential

receivers can receive data up to 5Mbps.

Decoder

The SP502 has the ability to change the inter-

face mode of the drivers or receivers via an 8–bit

switch. The decoder for the drivers and receiv-

ers is not latched; it is merely a combinational

logic switch. The codes shown in Tables 1 and

2 are the only specified, valid modes for the

SP502. Undefined codes may represent other

interface modes not specified or random out-

puts (consult the factory for more information).

The drivers are controlled with the data bits

labeled TDEC

3–TDEC0. The drivers can be put

into tri-state mode by writing 0000 to the driver

decode switch. The receivers are controlled with

data bits RDEC

3–RDEC0; the code 0000 written

to the receivers will place the outputs in an

undetermined state. All receivers, with the ex-

ception of SCT, do not have tri-state capability;

the outputs will either be HIGH or LOW de-

pending upon the state of the receiver input.

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