H8SLASH3028F datasheet(258/923 Pages) RENESAS

258 / 923 page

Rev. 2.00, 09/03, page 228 of 890

Activation by External Request: If an external request (

DREQ pin) is selected as an activation

source, the

DREQ pin becomes an input pin and the corresponding TEND pin becomes an output

pin, regardless of the port data direction register (DDR) settings. The

DREQ input can be level-

sensitive or edge-sensitive.

In short address mode and normal mode, an external request operates as follows. If edge sensing is

selected, one byte or word is transferred each time a high-to-low transition of the

DREQ input is

detected. If the next edge is input before the transfer is completed, the next transfer may not be

executed. If level sensing is selected, the transfer continues while

DREQ is low, until the transfer

is completed. The bus is released temporarily after each byte or word has been transferred,

however. If the

DREQ input goes high during a transfer, the transfer is suspended after the current

byte or word has been transferred. When

DREQ goes low, the request is held internally until one

byte or word has been transferred. The

TEND signal goes low during the last write cycle.

In block transfer mode, an external request operates as follows. Only edge-sensitive transfer

requests are possible in block transfer mode. Each time a high-to-low transition of the

DREQ

input is detected, a block of the specified size is transferred. The

TEND signal goes low during the

last write cycle in each block.

Activation by Auto-Request: The transfer starts as soon as enabled by register setup, and

continues until completed. Cycle-steal mode or burst mode can be selected.

In cycle-steal mode the DMAC releases the bus temporarily after transferring each byte or word.

Normally, DMAC cycles alternate with CPU cycles.

In burst mode the DMAC keeps the bus until the transfer is completed, unless there is a higher-

priority bus request. If there is a higher-priority bus request, the bus is released after the current

byte or word has been transferred.

H8/3028F 数据表(PDF) 258 Page - Renesas Technology Corp