3.0 Pin Descriptions
RC224ATL/224ATLV
EmbeddedModem Family
Table 3-5. Hardware Interface Signal Definitions (4 of 5)
Label
I/O Type
Signal Name/Description
HDIS
HINT
DO
Host Bus Driver Disable. HDIS output is low when the host is reading data from the modem
over the host data bus (both HRD and HCS are low). HDIS is also used to disable the external
transceiver drivers whenever data is not being read from the modem.
DO
Host Bus Interrupt. HINT output is 16C450-compatible output indicating interrupt status and
is enabled by the OUT2 bit set to a 1 in the Modem Control Register.
Telephone Line Interface
TXA1
TXA2
O(DF)
Transmit Analog 1 and 2. The TXA1 and TXA2 outputs are differential outputs. A 600 Ω
telephone coupling transformer may be driven directly without the need for external discrete
buffer amplifiers.
Both TXA1 and TXA2 outputs are turned off when the transmitter is disabled or during
local analog loopback.
RXA
VC
I(DA)
OA
Receive Analog. RXA is a single-ended receive data input from the telephone line interface.
Centerpoint Voltage. A +2.5 VDC centerpoint voltage derived from an internal reference
voltage. The TXA1 and TXA2 outputs are biased at VC.
TLKRELAY
DO
Talk/Data Relay Driver. TLKRELAY is an open drain output which can directly drive a relay
with greater than 360 Ω coil resistance and has “must operate” voltage of no greater than 4.0
VDC. A heavier load, such as an electro-mechanical relay, requires the use of an external
transistor. An external diode should be provided across the relay coil.
The TLKRELAY output is clamped off during power-on reset or the sleep mode. The
TLKRELAY output is activated and deactivated at the same time as the OHRELAY output.
In a typical application, TLKRELAY ON opens the normally closed Talk/Data relay and
disconnects the handset from the telephone line.
OHRELAY
DO
Off-Hook Relay Driver. OHRELAY is an open drain output which can directly drive a relay with
greater than 360 Ω coil resistance and has “must operate” voltage of no greater than 4.0
VDC. A heavier load, such as an electro-mechanical relay, requires the use of an external
transistor. An external diode should be provided across the relay coil.
The OHRELAY output is clamped off during power-on reset or the sleep mode. In a typical
application, OHRELAY ON closes the normally open Off-Hook relay and connects the modem
to the telephone line (off-hook).
RING
A/A1
DI
Ring Detector. RING is a TTL-compatible input used to indicate to the modem that a 15.3 Hz
to 63 Hz ringing signal is present.
The signal (a 4N35 optoisolator compatible output) into the RING input should not
respond to a voltage less than 40 VRMS, 15 Hz to 68 Hz, appearing across TIP and RING with
respect to ground.
A low-going edge on the RING input also removes the modem from the sleep mode.
DO
Key Telephone Hold Indicator. A/A1 output low indicates that the telephone line is in use
when used on multi-line key telephones.
3-18
Conexant
D224ATLVDSC
CONEXANT [ CONEXANT SYSTEMS, INC ]
