MB86391 Datasheet, PDF (32/69 Pages) Fujitsu Component Limited. – MPEG2 1chip Audio/Video Encoder

3.1.2.2 External Boot ROM Read
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BCLK(O)
XBREQ(I)
XBMREQ(I)
XBGRNT(O)
XRDWR( I/O)
XAS( I/O)
ADRS27:26, 17:2(I/O)
All ‘ H’
RA
XCS0(O)
XREADY( I/O)
D31:0( I/O)
All ‘ H’
XBUSEN(O)
BUSDIR(O)
RA
RD
All ‘ H’
All ‘ H’
Fig. 3.1.2.2: External boot ROM access timing (Read)
(1) With XCS0 asserted, the MB86391 selects the external boot ROM, sets BUSDIR to 'L' (read
direction) and XREADY to Hi−Z, and asserts XBUSEN to prepare for accessing.
(2) In conjunction with XAS, the MB86391 outputs valid data to ADRS27:26, 17:2 (let the external
boot ROM output read data to the data bus after confirming XCS0).
(3) After proper wait cycles, the MB86391 reads data and negates XCSO to cancel the selection.
(4) The MB86391 sets BUSDIR to ‘H’ (write direction), negates the XBUSEN and XREADY signals,
and resets to its normal state.
Note: The number of read wait cycles can be set in the boot program according to the
ROM in use. When defaulted, accessing is done with 30 wait cycles.
MB86391
Product Specification
Rev. 1.1
12, November 2001
28