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Serial Communication Controller
Sanity Timer
Bus Timer
Download Operation
System Initialization
NTBK51 Downloadable D-channel handler
The serial controller is the Zilog Z16C35 and is referenced as the Integrated
Controller (ISCC). The ISCC includes a flexible Bus Interface Unit (BIU)
and four Direct Memory Access (DMA) channels, one for each receive and
transmit. The DMA core of the ISCC controls the data transfer between local
RAM and the communication ports.
A sanity timer is incorporated on the DDCH to prevent the MPU from getting
tied-up as the result of a hardware or software fault. The sanity timer permits
the DDCH to reset itself should it enter into an infinite loop.
The bus timer presents an error signal to the MPU if an attempt to access a
device did not receive acknowledgment within the bus time-out period of 120
microseconds.
Downloading may be performed in either of two modes: background or
maintenance. Before any downloading can take place, a D-channel link must
be configured. The following situations may lead to software downloading:
•
during initialization when new software is installed
•
when enabling the card or application
•
during card reset (due to loss of software, corruption)
•
during a background audit
When new base or application software is installed on an Option 11C, the
downloading decision is made during system initialization. Actual MSDL
base software downloading is done in background mode which may take
several minutes to complete, depending on the traffic of the switch and the
size of the MSDL base software.
Option 11C and 11C Mini
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