MT90812 Mitel Networks Corporation, MT90812 Datasheet - Page 46

• Manufacturer Part Number: MT90812
• Description: Integrated Digital Switch (IDX)
• Manufacturer: Mitel Networks Corporation

MT90812
The second condition occurs if the Auto-hunt circuit manages to cycle back to monitor a peripheral which is
already the currently active receive channel. Because the peripheral continues to
during the time when it is being acknowledged with a go-ahead from the RX circuitry, it is important that flags
not be detected twice for the same request. This condition is prevented by disabling scanning on a currently
active receive channel.
The third condition that causes the Auto-hunt circuit to skip a channel, is if it has been locked out by the
system. This allows the system to independently disable reception from any channel. On reset, all 16 D-
channels are locked out, and the system must specify which channels are to be enabled for receive activity.
The two HDLC CTRL Lockout registers are described in Section 22.30 and Section 22.31.
The fourth condition that will cause the Auto-hunt circuit to skip a channel occurs when the scanned-channel
number is the same as an active TX channel. The channel is skipped in this case to reduce the contention
between a system transmit packet and the transmission of a CTS. If a flag has been detected before the
transmitter goes active on the same channel, then the contention, described in “TX and RX Handshaking” on
page 38, will occur. However, if the transmitter goes active at any point before a flag is detected, then
contention will be avoided.
14.1.7
A receive packet will be terminated when the HDLC controller asserts the REOP strobe for one bit period, one
bit time after the closing flag is received. If desired, the system may assert its own SREOP flag via the micro
interface. The SREOP bit is in “HRA CTRL Register 2 (HC2)” on page 71. This flag has the same effect as the
normal REOP strobe, but may be written asynchronously and will be cleared by the RX circuit after it has been
acted upon. In either case, a receive end-of-packet will cause RXACT to go low, disabling RxCEN.
15.0 C-Channel Data
C-Channel access for Codec or DNIC control is provided through Message Mode (refer to “Connection
Memory” on page 10). The C-Channel information can be read from Data Memory or written to Connect
Memory.
C-Channel data status information is very static. Therefore, the interface as provided via Message Mode is
single buffered. Hence, the C-channel information may change every frame.
16.0 Tone Generation
The MT90812 generates the standard 16 DTMF frequencies within +/- 0.6% of the nominal standard
frequencies. Table 13 shows the standard DTMF frequencies, the coefficient used to generate the closest
frequency, the actual frequency generated and the percent deviation of the generated tone from the nominal.
42
Group
Tone
High
Low
Receive Packet Termination
Frequency Hz
1209
1336
1477
1633
697
770
852
941
Table 13 - DTMF Frequencies
Coefficient
6DH
8DH
A9H
59H
62H
78H
96H
9FH
Actual Frequency
1203.12
1343.75
1484.38
1640.62
695.31
765.63
851.56
937.50
Advance Information
send request-to-sends
% Deviation
+0.58%
+0.50%
+0.47%
-0.24%
-0.56%
-0.05%
-0.37%
-0.49%