Nortel Networks Circuit Card - Manual (Page 766)

Page 766 of 906 NTAK93 D-channel Handler Interface daughterboard
553-3001-211 Standard 3.00 August 2005
DMA controller
A Z80A-DMA chip controls the data transfer between local RAM memory
and communication ports. The DMA channels are only used in the receive
direction (from line to SSC), not in the transmit direction.
Random Access Memory (RAM)
A total of 32 KBytes of RAM space for each pair of ports is used as the
communication buffer and for firmware data storage.
Read Only Memory (ROM)
A total of 32K bytes of ROM space for each pair of ports is reserved as a code
section of the DCH-PORT firmware.
LAPD data link/asynchronous controller
One chip controls each pair of independent communication ports. It performs
the functions of serial-to-parallel and parallel-to-serial conversions, error
detection, and frame recognition (in HDLC). The parameters of these
functions are supplied by the DCH-PORT firmware.
Counter/timer controller
Two chips are used as real-time timers and baud-rate generators for each pair
of communication ports.
Software interface circuit
This portion of the circuit handles address/data bus multiplexing, the
interchange of data, commands, and status between the on board processors
and software. It includes transmit buffer, receive buffer, command register,
and status register for each communication channel.
DPNSS/DCHI Port
The mode of operation of the DCH-PORT is controlled by a switch setting on
the NTAK09/NTBK50. For DPNSS the switch is ON; for DCHI it is OFF.