SP504 Sipex, SP504 Datasheet - Page 16

• Manufacturer Part Number: SP504
• Description: WAN Multi-Mode Serial Transceiver
• Manufacturer: Sipex

Receivers
The SP504 has seven (7) independent receivers
which can be programmed for the different
interface modes. Control for the mode selection
is done via a 4–bit control word that is indepen-
dent from the driver control word. The coding
for the drivers and receivers is identical. There-
fore, if the modes for the drivers and receivers
are supposed to be identical in the application,
the control lines can be tied together.
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 sup-
port the requirements of clock, data, and control
line receivers. Table 2 shows 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 2.4V. 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
3kΩ to 7kΩ. RS-232 receivers are used in RS-
232 mode for all data, clock and control signals.
They are also used in V.35 mode for control line
signals such as CTS and DSR.
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 in RS-449, EIA-530,
EIA-530A and V.36 modes as Category II sig-
nals as indicated by their corresponding specifi-
cations.
The third type of receiver is a differential which
supports RS-485. The RS-485 receiver has an
input impedance of 15kΩ and a differential
threshold of ±200mV. 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.
Rev: A Date:1/27/04
SP504 Multi–Mode Serial Transceivers
16
RS-422 receivers are used in RS-449,
EIA-530, EIA-530A and V.36 as Category I
signals for receiving clock, data, and some con-
trol line signals. The differential receivers can
receive data up to 10Mbps.
The RS-485 receivers are also used for the V.35
mode. Unlike the older implementations of
differential or V.35 receivers, the SP504 con-
tains an internal resistor termination network
that ensures a V.35 input impedance of 100Ω
(±10Ω) and a short-circuit impedance of 150Ω
(±15Ω). The traditional V.35 implementations
required external termination resistors to acheive
the proper V.35 impedances. The internal net-
work is connected via low on-resistance FET
switches when the decoder is changed to V.35
mode. The termination network is transparent
when all other modes are selected. The V.35
receivers can operate up to 10Mbps.
All receivers include a fail-safe feature that
outputs a logic HIGH when the receiver inputs
are open. For single-ended RS-232 receivers,
there are internal 5kΩ pull-down resistors on the
inputs which produces a logic HIGH ("1") at the
receiver outputs. The single-ended RS-423 re-
ceivers 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 differen-
tial receivers have the same internal pull-up
device on the non-inverting input which pro-
duces a logic HIGH ("1") at the receiver output.
The three differential receivers when config-
ured in V.35 mode (RxD, RxC & SCT) do not
have fail-safe because the internal termination
resistor network is connected.
Decoder
The SP504 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 control word can be externally latched
either HIGH or LOW to write the appropriate
code into the SP504. The codes shown in Tables
1 and 2 are the only specified, valid modes for
the SP504. Undefined codes may represent other
interface modes not specified (consult the fac-
© Copyright 2004 Sipex Corporation