Serial Interface - Nortel Circuit Card Installation Manual

Page 394 of 906
Micro Processing Unit (MPU)
Memory

Serial interface

553-3001-211 Standard 3.00
NT6D80 MSDL card
The MPU, which is based on a Motorola 68020 processor, coordinates and
controls data transfer and port addressing, communicating via the CPU bus
with the system. Prioritized interrupts tell the MPU which tasks to perform.
The MSDL card contains two megabytes of Random Access Memory (RAM)
for storing downloaded peripheral software that controls MSDL port
operations. The MSDL card includes the shared RAM that is used as a
communication interface buffer between the CPU and the MPU.
The MSDL Flash Erasable Programmable Read Only Memory (Flash
EPROM) also includes the peripheral software to protect it against a power
failure or reset. MSDL can copy peripheral software directly from the Flash
EPROM after power up or reset instead of requesting that the system CPU
download it.
The MSDL card also contains Programmable Read Only Memory (PROM)
for firmware that includes the bootstrap code.
The MSDL card provides one monitor port and four programmable serial
ports that can be configured for the following various interfaces and
combinations of interfaces:
• synchronous ports 0–3
• asynchronous port 0
• DCE or DTE equipment emulation mode
• RS-232 or RS-422 interface
Transmission mode – All four ports of the MSDL can be configured for
synchronous data transmission by software. Port 0 can be configured for
asynchronous data transmission for CRT, TTY, and printer applications only.
August 2005