ST92196A STMicroelectronics, ST92196A Datasheet - Page 100

• Manufacturer Part Number: ST92196A
• Description: 8/16-bit Mcu For Tv Applications With Up To 96k Rom, On-screen-display And 1 Or 2 Data Slicers
• Manufacturer: STMicroelectronics

MULTIFUNCTION TIMER (Cont’d)
8.3.5.6 DMA End Of Block Interrupt Routine
An interrupt request is generated after each block
transfer (EOB) and its priority is the same as that
assigned in the usual interrupt request, for the two
channels. As a consequence, they will be serviced
only when no DMA request occurs, and will be
subject to a possible OUF Interrupt request, which
has higher priority.
The following is a typical EOB procedure (with
swap mode enabled):
– Test Toggle bit and Jump.
– Reload Pointers (odd or even depending on tog-
– Reset EOB bit: this bit must be reset only after
– Verify the software protection condition (see
– Read the corresponding Overrun bit: this con-
– Reset the corresponding pending bit.
– Reenable DMA with the corresponding DMA
gle bit status).
the old pair of pointers has been restored, so
that, if a new EOB condition occurs, the next pair
of pointers is ready for swapping.
Section
firms that no DMA request has been lost in the
meantime.
mask bit (must always be done after resetting
the pending bit)
8.3.5.7).
– Return.
WARNING: The EOB bits are read/write only for
test purposes. Writing a logical “1” by software
(when the SWEN bit is set) will cause a spurious
interrupt request. These bits are normally only re-
set by software.
8.3.5.7 DMA Software Protection
A second EOB condition may occur before the first
EOB routine is completed, this would cause a not
yet updated pointer pair to be addressed, with con-
sequent overwriting of memory. To prevent these
errors, a protection mechanism is provided, such
that the attempted setting of the EOB bit before it
has been reset by software will cause the DMA
mask on that channel to be reset (DMA disabled),
thus blocking any further DMA operation. As
shown above, this mask bit should always be
checked in each EOB routine, to ensure that all
DMA transfers are properly served.
8.3.6 Register Description
Note: In the register description on the following
pages, register and page numbers are given using
the example of Timer 0. On devices with more
than one timer, refer to the device register map for
the adresses and page numbers.
- MULTIFUNCTION TIMER (MFT)
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