SP502 Datasheet, PDF (13/32 Pages) Sipex Corporation – 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 100kΩ 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 5kΩ 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
4kΩ, 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
15kΩ 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
100Ω. In order to meet the V.35 input imped-
ance of 100Ω, 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 TDEC₃–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 RDEC₃–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.
Rev. 7/21/03
SP502 Multi-Mode Serial Transceiver
13
© Copyright 2003 Sipex Corporation