Chain Transfer When Counter = 0 - Hitachi H8S/2378, H8S/2378R Series Hardware Manual

9. Each time a TGRA compare match occurs, the next output value is transferred to NDR and the
set value of the next output trigger period is transferred to TGRA. The activation source TGFA
flag is cleared.
10. When the specified number of transfers are completed (the TPU transfer CRA value is 0), the
TGFA flag is held at 1, the DTCE bit is cleared to 0, and a TGIA interrupt request is sent to the
CPU. Termination processing should be performed in the interrupt handling routine.
9.7.3

Chain Transfer when Counter = 0

By executing a second data transfer, and performing re-setting of the first data transfer, only when
the counter value is 0, it is possible to perform 256 or more repeat transfers.
An example is shown in which a 128-kbyte input buffer is configured. The input buffer is assumed
to have been set to start at lower address H'0000. Figure 9.12 shows the chain transfer when the
counter value is 0.
1. For the first transfer, set the normal mode for input data. Set fixed transfer source address
(G/A, etc.), CRA = H'0000 (65,536 times), and CHNE = 1, CHNS = 1, and DISEL = 0.
2. Prepare the upper 8-bit addresses of the start addresses for each of the 65,536 transfer start
addresses for the first data transfer in a separate area (in ROM, etc.). For example, if the input
buffer comprises H'200000 to H'21FFFF, prepare H'21 and H'20.
3. For the second transfer, set repeat mode (with the source side as the repeat area) for re-setting
the transfer destination address for the first data transfer. Use the upper 8 bits of DAR in the
first register information area as the transfer destination. Set CHNE = DISEL = 0. If the above
input buffer is specified as H'200000 to H'21FFFF, set the transfer counter to 2.
4. Execute the first data transfer 65,536 times by means of interrupts. When the transfer counter
for the first data transfer reaches 0, the second data transfer is started. Set the upper 8 bits of
the transfer source address for the first data transfer to H'21. The lower 16 bits of the transfer
destination address of the first data transfer and the transfer counter are H'0000.
5. Next, execute the first data transfer the 65,536 times specified for the first data transfer by
means of interrupts. When the transfer counter for the first data transfer reaches 0, the second
data transfer is started. Set the upper 8 bits of the transfer source address for the first data
transfer to H'20. The lower 16 bits of the transfer destination address of the first data transfer
and the transfer counter are H'0000.
6. Steps 4 and 5 are repeated endlessly. As repeat mode is specified for the second data transfer,
an interrupt request is not sent to the CPU.
Rev. 1.0, 09/01, page 399 of 904