Pin Number Function
FX809
J/LG/LS
1
2
3
Xtal: The output of the on-chip clock oscillator. External components are required at this input
when a Xtal input is used. See Figure 2, INSET.
Xtal/Clock: The input to the on-chip clock oscillator inverter. A Xtal or externally derived clock
should be connected here. See Figure 2, INSET.
Interrupt Request (IRQ): The output of this pin indicates an interrupt condition to the
µController, by going to a logic “0.” This is a “wire-or able” output, enabling the connection of
up to 8 peripherals to 1 interrupt port on the µController. This pin has a low-impedance
pulldown to logic “0” when active and a high-impedance when inactive. The system IRQ line
requires a 'pull-up' resistor to VDD.
The conditions that cause interrupts are indicated in the Status Register and are shown below:
Tx Idle
Rx Data Ready
Tx Data Ready
Rx SYNC Detect
Rx SYNC Detect
Interrupt outputs can be disabled by bit 3 of the Control Register.
No Internal connection.
4
5
6
No Internal connection.
Rx Freeformat: Used in the Rx mode, this input, when a logic “0,” allows received data to be
read from the Rx Data Buffer via the Reply Data line without having to acheive byte
synchronization (SYNC/SYNC) first. Data will continue to be available after this input goes to a
logic “1” until either a SYNC or SYNC Prime bit is set or the the modem set to Tx mode.
When held at a logic “1” the modem operates normally. This pin has an internal 1MΩ pullup
resistor.
NOTE: If this input is held at a logic “0” in the Tx mode, the Rx Data Ready bit in the Status
Register may occasionally be set, but not cause an interrupt. If this input is a logic “0” when
going into the Rx mode, an Rx Data Ready interrupt may be generated immediately, in this
case the first byte of Rx data should be ignored.
VBIAS : The internal circuitry bias line, held at VDD/2 this pin must be decoupled to VSS by
capacitor C3, see Figure 2.
7
Amp In: The inverting input to the on-chip uncommitted amplifier .
Amp Out: The output of the on-chip uncommitted amplifier.
8
9
Rx In: The 1200 baud, 1200Hz/1800Hz, received FFSK signal input. The input signal to this
pin must be a.c. coupled via capacitor C4, see Figure 2.
10
No Internal connection.
11
12
VSS: Negative Supply (GND).
CMLMICRO [ CML MICROCIRCUITS ]
