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ACS103

3 Channel, Synchronous or Asynchronous Single Fiber Modem

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or 6.0 kHz using the recommended crystal frequency

- 9.216 MHz. The sample frequency for 'Double'

mode is: (crystal freq)/3072, or 3 kHz using the

recommended crystal of 9.216 MHz.

The output filters for XO1/2/3 require a minimum

over-sampling of 6 on data presented to the XI1/2/3

inputs.

consequently the jitter on the output RxD. The

sample frequency is always 1/108 of the chosen

clock frequency in 'Standard' mode and 1/216 in

'Double' mode. In ACS101 emulation mode the

sample frequency is 1/36 of crystal clock frequency

in 'Standard' mode and 1/72 of the crystal clock

frequency in 'Double' mode.

In ACS101 mode the XI3 input is internally disabled Integrating Capacitor

and the XO3 output is forced into the high impedance

state.

The ACS103 requires the use of an integrating

ceramic capacitor of value 22 nF - 33 nF between

RSS High - Modem Handshake Mode.

pins CNT and GND for a crystal oscillator frequency

range of 5 - 10 MHz.

In modem handshake mode the control signals are

used as conventional handshake signals between the DCDB

DTE (terminal) and the DCE (modem):

DSR (Data Set Ready) DCE à DTE.

The Data Carrier Detect (DCDB) signal goes Low

when the modems are locked and ready for data

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transmission.

The DCE is powered up and asserts a Low (active

level) on DSR. The DTE is informed that it is PORB

connected to a “live” DCE.

The PORB pin is a single-pin alternative to the reset

DTR (Data Terminal Ready) DTE à DCE.

combination DM3 = 0, DM2 = 0, DM1 = 1. If left

unconnected the input pulls High to the operational

The DTE is powered up and asserts a Low (active state. Selecting reset using DM1-DM3 or holding

level) on DTR. The DCE is informed that it is PORB Low turns off the LED and most of the digital

connected to a “live” DTE. If DTR is set High, the logic. The device has been designed to power-up

DCE responds by taking DCDB High.

correctly and operate without the aid of PORB.

RTS (Request to Send) DTE à DCE.

Transmission Clock TxCL

The DTE recognises that synchronisation has been

achieved (DCDB active) and asserts a Low (active

level) on RTS. This constitutes a request by the DTE

to send data to the far-end modem.

The ACS103 gives a choice between internally and

externally generated transmission clocks (see Figure

2. Timing diagrams for set-up and hold

specifications).

CTS (Clear to Send) DCE à DTE.

The DCE recognises the active RTS signal and

responds by asserting a Low (active level) on CTS. If

RTS is set High the DCE responds by bringing CTS

High.

DCDB (Data Carrier Detect) DCE à DTE.

When synchronisation is achieved between DCEs

the DCDB signal is set Low (active level). If

synchronisation is lost the DCE sets DCDB and CTS

High.

Crystal Clock

A crystal may be connected between the pins XLI and

XLO. Alternatively, XLI may be driven directly by an

external clock. The operational frequency range is

5 MHz to 10 MHz, though communicating devices

must be driven at the same nominal frequency with a

tolerance of 100 ppm. In synchronous mode the

frequency should be 9.216 MHz, resulting in the

standard range of synchronous communication

frequencies selected by DR1-DR4.

For asynchronous operation, the choice of crystal

clock frequency dictates the sample rate of the

asynchronous data appearing at the input TxD, and

When the CKC pin is held Low, TxCL is configured as

an output producing a clock at the frequency defined

by DR1-DR4. Data is clocked into the device on the

rising edge of the internally supplied clock.

When the CKC pin is held High, TxCL is configured

as an input, and will accept an externally produced

transmission clock with a tolerance of up to 500 ppm

with respect to the transmission rate determined by

DR1-DR4. The ACS103 performance is at its best

when external changes on input pins are

synchronised with internal clocks. Therefore,

superior performance is likely when using the

internally generated data transmission clock. If

however, an externally generated transmission clock

is used, then TxCL and TxD are generally

asynchronous to the ACS103 internal clocks,

performance in this case will be enhanced by limiting

the edge speed of the TxCL and TxD signals so that

they are greater than 150 ns. The modem has been

designed to cope with very slow edges on inputs,

without fear of metastability problems.

Receive Clock RxCL

In synchronous mode data is valid on the rising edge

of RxCL clock (see Figure 2. Timing diagrams). To

ensure that the average receive frequency is the

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ACS103 Issue 2.03 May 1996.

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