Specifications

ASM-10/8 Installation and Operation Manual Chapter 1 Introduction
Functional Description 1-7
Modulation Timing
This circuit supplies the transmit clock signal to the encoder.
The following clock sources are available:
• INT.CK (internal clock) – from the modem's internal crystal oscillator)
• EXT.CK (external clock) – from DTE, pin 24
• RCV.CK (receive clock) – recovered from the received signal
• ASYNC – asynchronous timing for working with the async to sync converter in
asynchronous applications.
Timing options are selected using the XMT TIMING jumpers.
Async to Sync Converter
ASM-10/8 has an internal asynchronous to synchronous converter (used for
asynchronous data).
Asynchronous transmission is provided by internal conversion from asynchronous
to synchronous mode in compliance with ITU V.22 bis. In this standard, the
modem compensates for frequency deviation between the modem and the DTE
by adjusting the length of the stop bit of the async character. If the modem's
frequency is higher than the DTE, the local converter extends the stop bit. If the
modem's frequency is lower than the DTE, the local converter deletes one stop bit
in every four (25%) or eight (12.5%) characters. The remote converter will add a
shorter stop bit (shorter by 12.5% or 25%) before sending the data to the remote
DTE.
Shortening the stop bits by 12.5% is suitable for frequency deviations up to 1.1%
and shortening the stop bits by 25% is suitable for frequency deviations up to
2.3%.
XMT Level and XMT Filter (Optional)
Four options are available for the XMT level (signal level): 0, -3, -6, -9 dBm.
An optional output filter for the line is available. This filter complies with
Bell 43401 standard and meets British Telecom requirements.
Receiver
The receiver comprises several circuits, as shown in the block diagram (see
Figure 1-6).
• The receive filter removes all the out-of-band frequencies.
• The automatic equalizer comprises several equalizers which are activated
according to baud rate.
• The digital AGC automatically compensates for the attenuation of the line.