SP505 Datasheet, PDF (21/35 Pages) Sipex Corporation – WAN Multi-Mode Serial Transceiver

serial interface. As the operating mode of the
receivers is changed, the electrical characteris-
tics will change to support 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
— V.28, V.10, and V.11.
V.28 Receivers
The V.28 receiver is single–ended and accepts
V.28 signals from the V.28 driver. The V.28
receiver has an operating voltage range of +15V
and can receive signals down to +3V. The input
sensitivity complies with RS-232 and V.28 speci-
fications at +3V. The input impedance is 3kΩ to
7kΩ in accordance to RS-232 and V.28 over a
+15V input range. The receiver output pro-
duces a TTL/CMOS signal with a +2.4V mini-
mum for a logic "1" and a +0.8V maximum for
a logic "0". V.28 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: CTS, DSR, LL, and RL. The V.28
receivers can operate to at least 120kbps.
V.10 Receivers
The V.10 receivers are also single–ended as
with the V.28 receivers but have an input thresh-
old as low as +200mV. The input impedance is
guaranteed to be greater than 4KΩ, with an
operating voltage range of +7V. The V.10 re-
ceivers can operate to at least 120kbps. V.10
receivers are used in RS-449, EIA-530, EIA-
530A and V.36 modes as Category II signals as
indicated by their corresponding specifications.
V.11 Receivers
The third type of receiver is a differential which
supports V.11 and RS-485 signals. This re-
ceiver has a typical input impedance of 10kΩ
and a typical differential threshold of +200mV,
which complies with the V.11 specification.
Since the characteristics of the V.11 receivers
are actually subsets of RS-485, the V.11 receiv-
ers can accept RS-485 signals. However, these
receivers cannot support 32-transceivers on the
signal bus due to the lower input impedance as
specified in the RS-485 specification. Three
receivers (RxD, RxC, and SCT) include a typi-
cal 120Ω cable termination resistor across the A
and B inputs. The resistor for the three receivers
is switched on when the SP505 is configured in
a mode which uses V.11 receivers. The V.11
cable termination resistor is switched off when
the receiver is disabled or in another operating
mode not using V.11 receivers. The V.11 re-
ceivers are used in X.21, RS-449, EIA-530,
EIA-530A and V.36 as Category I signals for
receiving clock, data, and some control line
signals not covered by Category II V.10 circuits.
The differential receivers can receive signals
over 10Mbps.
V.35 Receiver
The V.11 receivers are also used for the V.35
mode. Unlike the older implementations of
differential receivers used for V.35, the SP505
contains an internal resistor termination net-
work that ensures a V.35 input impedance of
100Ω (+10Ω) and a short-circuit impedance of
150Ω (+15Ω). The traditional V.35 implemen-
tations required external termination resistors to
achieve the proper V.35 impedances. The inter-
nal network is connected via low on-resistance
FET switches when the decoder is changed to
V.35 mode. These FET switches can accept
input signals of up to +15V without any forward
biasing and other parasitic affects. The V.35
termination resistor network is switched off
when the receiver is disabled either by the de-
coder or receiver enable pin. The termination
network is transparent when all other modes are
selected. The V.35 receivers can operate over
10Mbps.
To Inverting Input
of Receiver
V.11 TERMINATION
MODE [0100]
rON = 20Ω
51Ω
51Ω
rON = 1Ω
124Ω
RIN [a]
V.35 MODE
rON = 1Ω
To Non-Inverting
Input of Receiver
RIN [b]
Figure 51. Simplified R_IN Termination Circuit
Receiver Enable and Output
Only one receiver includes an enable line. The
SCTEN input for the SCT receiver can enable or
tri-state the output of the receiver. When the pin
is at a logic "0", the receiver output is high
impedance and any input termination internal
connected is switched off. The inputs will be at
approximately 10kΩ during tri-state.
Rev: A Date: 1/27/04
SP505 Multi–Mode Serial Transceiver
21
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