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In repeat mode ETCRH is used as the transfer counter while ETCRL holds the initial transfer
count. ETCRH is decremented by 1 at each transfer until it reaches H'00, then is reloaded from
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ETCRL. MAR is also restored to its initial value, which is calculated from the DTSZ and DTID
bits in DTCR. Specifically, MAR is restored as follows:
← MAR – (–1)
MAR
ETCRH and ETCRL should be initially set to the same value.
In repeat mode transfers continue until the CPU clears the DTE bit to 0. After DTE is cleared to 0,
if the CPU sets DTE to 1 again, transfers resume from the state at which DTE was cleared. No
CPU interrupt is requested.
As in I/O mode, MAR and IOAR specify the source and destination addresses. MAR specifies a
24-bit source or destination address. IOAR specifies the lower 8 bits of a fixed address. The upper
16 bits are all 1s. IOAR is not incremented or decremented.
Figure 8-6 illustrates how repeat mode operates.
Address T
Address B
DTID
DTSZ
· 2
· ETCRL
Transfer
1 byte or word is
transferred per request
Legend
L = initial setting of MAR
N = initial setting of ETCRH and ETCRL
Address T = L
Address B = L + (–1)
Figure 8-6 Operation in Repeat Mode
213
DTID
DTSZ
• (2
• N – 1)
IOAR
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