HD6417616 RENESAS [Renesas Technology Corp], HD6417616 Datasheet - Page 540

• Manufacturer Part Number: HD6417616
• Description: 32-Bit RISC Microcomputer SuperH™ RISC engine Family/SH7600 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

Section 11 Direct Memory Access Controller (DMAC)
11.3.9
Purpose of New Specifications for BH
external bus, Grew logic must be used externally because the SH7616 is not equipped with a PCI
bus interface.
The PCI bus uses burst transfer principally, and performance is poor if data is transferred in small
increments.
Due to these properties of the PCI bus, it is necessary to use Grew logic externally to compare the
present address and the next address and determine whether burst transfer is possible. However,
the size of the external Grew logic increases if address comparisons are required, and there is also
the possibility that delays may interfere with timing requirements.
The specifications for BH have therefore been updated in order to solve these problems. Now if
burst transfer is possible using the present address this information is passed to the external Grew
logic. This provides enhanced support for PCI bus connections.
Register Settings When Using BH
is selected using the DMAC built into the SH7616. However, it is not output when SDRAM or
DRAM are accessed. When using the 16-byte transfer mode, specify auto-request mode or the
external request mode with edge detection. If external request mode with level detection or on-
chip module request mode is specified, operation is not guaranteed.
To use BH, the settings for the CHCR0 register or CHCR1 register in the on-chip DMAC of the
SH7616 must be as shown in figure 11.43. BH is not output unless the settings for the CHCR0
register or CHCR1 register are as indicated in figure 11.42.
Rev. 2.00 Mar 09, 2006 page 514 of 906
REJ09B0292-0200
Transfer end when DME = 0 in DMAOR
Clearing the DME bit in DMAOR forcibly aborts the transfers on both channels at the end of
the current bus cycle. When the transfer is the final transfer, TE = 1 and the transfer ends.
BH
BH Pin Output Timing
BH
BH
BH Pin: BH is output from only when the 16-byte transfer mode
BH
BH
BH
BH
BH: When the SH7616 is connected to the PCI bus as an