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

mode selection is done via a 4–bit control
word, which is the same as the driver's 4-bit
control word.
Like the drivers, the receivers are prear-
ranged for the specific requirements of
the synchronous serial interface. As the
operating mode of the receivers is changed,
the electrical characteristics 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 cir-
cuits — V.28, V.10, and V.11.
V.28 Receivers
The V.28 receiver is single–ended and ac-
cepts 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 specifications 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 produces a TTL/CMOS
signal with a +2.4V minimum 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 in-
put threshold as low as +200mV. The input
impedance is guaranteed to be greater than
4KΩ, with an operating voltage range of +7V.
The V.10 receivers 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 receiver 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 receivers 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 typical 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 receivers 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 implementa-
tions of differential receivers used for V.35,
the SP505 contains 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 achieve
the proper V.35 impedances. The internal
network is connected via low on-resistance
FET switches when the decoder is changed
to V.35 mode. These FET switches can ac-
cept 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 decoder 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 R eceiver
V.11 TERMINA TION
MODE [0100]
rON = 20Ω
51Ω
51Ω
rON = 1Ω
124Ω
R IN [a]
V.35 MODE
rON = 1Ω
To N on-Inverting
Input of R eceiver
R IN [b]
Figure 51. Simplified R_IN Termination Circuit
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