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Chapter 14 Automatic Transfer Controller
XIV - 13
13
14-3-4 Setting the Data Transfer Modes
Data transfer modes
There are two types of ATC1 transfers, standard and burst, and sixteen transfer modes. Set the transfer
mode in ATC1 control register 0 (AT1CNT0).
Standard and burst transfers
The ATC1 transfer modes are divided into standard transfer modes and burst transfer modes. There are
fourteen standard modes, 0 to D, and two burst modes, E and F.
In standard modes, the operation specified for that mode executes each time ATC1 is activated. When
the transfer ends, the value set in the transfer counter (AT1TRC) decrements and bus control returns to
the MCU core. This operation repeats until the transfer counter reaches x'00'. When this happens, ATC1
completes the final data transfer, then generates an interrupt (ATC1IRQ).
For instance, if the initial transfer counter value is x'05', and the ATC1 activation factor is set to a timer 0
interrupt, ATC1 is activated each time timer 0 overflows and the automatic transfer begins. After fifth
data transfers (activated by fifth timer 0 overflow) is complete, the transfer counter value becomes x'00',
an ATC1 interrupt occurs, and the operation ends. Timer 0 overflows occurring after this point do not
activate ATC1. For standard transfers, the program must set the transfer counter to the number of ATC1
activations required.
In burst modes, once ATC1 is activated, it transfers in one operation the number of bytes set in the
transfer counter (AT1TRC). After the burst transfer begins, the transfer counter decrements each time
ATC1 transfers one byte of data. When the counter reaches x'00', ATC1 generates an interrupt
(ATC1IRQ) and the burst transfer ends. For burst transfers, the program must set the transfer counter to
the number of data bytes in the burst transfer.
An external interrupt 0 can also be used to shut down ATC1 during a burst transfer. To enable this
function, set the burst transfer stop enable bit (BTSTP) in ATC1 control register 1 (AT1CNT1) to 1.
When BTSTP = 1, ATC1 data transfers stop when the external interrupt 0 interrupt request flag (IRQ0IR
flag in the IRQ0ICR register) is set. In an emergency shutdown, the transfer counter and memory pointer
save the values they contained prior to the shutdown. When the interrupt service routine ends, a new
activation factor restarts ATC1, and the burst transfer begins transferring data from the point at which it
stopped.
[ Table 14-1-2 Transfer Modes ]