MT90812 Mitel Networks Corporation, MT90812 Datasheet - Page 50

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

MT90812
Data is written to the FSK FIFO. Start and Stop bits are added to each byte. The FSK modulator generates two
output frequencies, representing the ‘marks’ and ‘spaces’. At 1200 baud, one bit is transmitted every 6
frames. The resulting PCM encoded signal is written to DM where it can be switched to any outgoing channel.
When an interrupt occurs the FTS bit is set in the Interrupt Status Register (INTS). The interrupt may be
enabled by setting the FTE bit in Interrupt Enable Register (INTE). An FSK interrupt may occur for two reasons.
When the FIS bit, in the Ringer and FSK Control Register (RFC), is Low, an interrupt is generated when the TX
FIFO is empty, when the FIS bit is High, an interrupt is generated at the end of transmission.
The FIFO empty interrupt will occur when the last byte has been read and before the byte has been
transmitted. FSK transmitter will finish transmitting this last byte 11 bits (73 1/3 frames) later and start the idle
state if the FIFO has not been refilled. The 11 bits include the start bit, 8 bits from the FIFO and 2 idle bits.
End of transmission must be confirmed before disabling the FSK transmitter or switching to another output
channel. The end of transmission can be selected by setting the FIS bit. End of transmission interrupt will occur
after 2 idle state bits have been transmitted. Subsequently end of transmission interrupts occur once every 8
idle state bits.
This interrupt can also be used by the system to count the number of bits sent in the channel seizure and mark
preamble before the FSK data. When the FSK transmitter is enabled, by setting the FEN bit in the FSK Control
Register, and the FIFO is not written to, the first end of transmission interrupt is after 2 idle state bits (13 1/3
frames). Subsequent interrupts are once every 8 bits (53 1/3 frames).
In addition to selecting the type of interrupt the Ringer and FSK Control Register (RFC) is used to select the
idle state of continuous ‘mark’ or continuous ‘space’, the ‘mark’ and ‘space’ frequency standard, and to turn on
or off the transmitter. Also, a ‘channel seizure’ signal of alternating ones and zero’s can be enabled. Refer to
the description of the “Ringer and FSK Control Register (RFC)” on page 58.
Programming sequence for on-hook data transmission (channel seizure + mark + data packet):
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46
1 - FSK modulator that generates two output frequencies, representing the ‘marks’ and
‘spaces’. Start and Stop bits are added to each byte.
2 - FSK transmitter outputs PCM coded signal.
Transmit Channel seizure
1.
2.
FEN initially 0 so that FSK transmit is disabled. Select end of transmission interrupt and enable.
FSK interrupt. Select channel seizure as idle state.
Enable transmission via FEN=1. Use end of transmission interrupt to count how many bits have
been transmitted. The first interrupt occurs after two idle state bits (13 1/3 frames) have been sent.
Uport Write
5F
07
H
H
Control Registers
Data Memory
FSKM
Figure 26 - Data Flow for FSK transmitter
1
FSK Transmitter
0100 1001
FSK FIFO
0
1
Parallel to Serial
PCM byte
2
Channel m
Output Stream
Advance Information
Connect Memory
5F
H
2
/
3