PEP Modular Computers PMC251, Manual

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PMC251 Functional Description
ID 19942, Rev. 0100 Page 2 - 4 ® PEP Modular Computers GmbH
2.2.1 Register Description
2.2.2 Watchdog Timer
A 512 ms watchdog timer triggers the on-board system reset generator at timeout. Once
enabled via the board control/status register, the watchdog timer cannot be reset by
software. It must be re-triggered via the corresponding bit in the board control/status
register periodically within the timeout period.
2.2.3 On-Board Bus Error Timer
A 128 µs timeout monitors the cycle lengths of data transfers to and from locations
beyond the CPU data bus buffer including the on-board I/O and PROFIBUS interface.
After a timeout occurs it generates an on-board BERR signal for error termination. This
timer is enabled/disabled via the board control/status register, which also supplies a tim-
eout status bit in order to identify bus errors generated by the on-board bus error timer.
There are two cases of bus error which are described in the following table.
Table 2-3: PMC251 Register Description
Name Value Access Description
WDG Read/Write Set by watchdog timer when timeout has been
reached. Used to differentiate between resets
caused by the watchdog and resets caused by a
reset button (power up resets can be identified
within the 68360)
S_BRB Read Boot jumper (S_BOOT) read back
BERR1 Read/Write Set by on-board bus error timer when timeout has
been reached. Used to identify BERR caused by
this timer.
EN_WDG 1 Read/Write Enable the watchdog timer. It can only be set
once, and remains enabled until the next reset.
TR_WDG 1 Read/Write Triggers the watchdog timer.
EN_BERR1 1 Read/Write Enables the on-board bus error timer. It also mon-
itors all on-board I/O cycles, including the time
from the VME bus request to the VME bus grant.
ABRB 1 Read ABORT read back
LED_G Read/Write General purpose LED driver
Table 2-4: Bus Error Description
Cause Timeout Enable/Disable Possible
Reserved Address BERR0 100 ns Permanently enabled
On-Board BERR1 128 µs Set in board control register