HD6417615 Hitachi Semiconductor, HD6417615 Datasheet - Page 487

• Manufacturer Part Number: HD6417615
• Description: Hardware Manual
• Manufacturer: Hitachi Semiconductor

External Request Mode: In this mode a transfer is started by a transfer request signal (DREQ)
from an external device. Choose one of the modes shown in table 11.4 according to the application
system. When DMA transfer is enabled (DE = 1, DME = 1, TE = 0, NMIF = 0, AE = 0), a transfer
is performed upon input of a DREQ signal.
Table 11.4 Selecting External Request Modes with the TA and AM Bits
TA
0
1
Note: External memory, memory-mapped external device.
Choose to detect DREQ either by the falling edge or by level using the DS and DL bits in CHCR0
and CHCR1 (DS = 0 is level detection, DS = 1 is edge detection; DL = 0 is active-low, DL = 1 is
active-high). The source of the transfer request does not have to be the data transfer source or
destination.
When 0 (level detection) is set to the DS bit of CHCR0 and CHCR1, set the TB bit to 0 (cycle-
steal mode) and set the TS1 and TS0 bits of CHCR0 and CHCR1 to either 00 (byte unit), 01 (word
unit), or 10 (long word unit).
When 0 is set to the DS bit of CHCR0 and CHCR1, when 1 (burst mode) is set to the TB bit of
CHCR0 and CHCR1, and when 11 (16 byte unit) is set to the TS1 and TS0 bits of CHCR1 and
CHCR1, operation is not guaranteed.
Table 11.5 Selecting the External Request Signal with the DS and DL Bits
DS
0
1
472
CHCR
AM
0
1
0
1
CHCR
DL
0
1
0
1
Transfer
Address Mode
Dual address
mode
Dual address
mode
Single address
mode
Single address
mode
External Request
Low-level detection (can only be set in cycle-steal mode)
High-level detection (can only be set in cycle-steal mode)
Falling-edge detection
Rising-edge detection
Acknowledge Mode
DACK output in read
cycle
DACK output in write
cycle
Data transferred from
memory to device
Data transferred from
device to memory
Source
Any*
Any*
External memory or
memory-mapped
external device
External device
with DACK
Destination
Any*
Any*
External device
with DACK
External memory or
memory-mapped
external device