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NTBK51 Downloadable D-channel Handler daughterboard Page 777 of 894
Circuit Card Description and Installation
Sanity timer
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. If the MPU encounters a
hardware or software fault and enters a continuous loop, the sanity timer
enables the DDCH to reset itself.
Bus timer
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 ms.
Download operation
Downloading is performed in either of two modes: background mode or
maintenance mode. Before a download takes place, a D-channel link must be
configured. The following situations 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 or corruption)
• during a background audit
System initialization
When new base or application software is installed on a CS 1000S,
CS 1000M Cabinet, and Meridian 1 PBX 11C Cabinet, the download
decision is made during system initialization. The actual MSDL base
software download is done in background mode and can take several minutes
to complete, depending on switch traffic and the size of the MSDL base
software.
Card enabling or application enabling
If a normal download enable command is executed, the MSDL base code and
application is conditionally downloaded to the DDCH card. This conditional