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Bus and Memory Control (BCU, MEMC)
Chapter 7
Preliminary User’s Manual U17566EE1V2UM00
7.4 Page ROM Controller
In page ROM mode the microcontroller reads consecutive data from one page
by inserting the wait cycles defined by PRC.PRW[2:0] instead of wait cycles
defined in registers DWC0 and DWC1.
The page ROM controller decides whether a page ROM cycle is on-page or
off-page. To do so, it buffers the address of the previous cycle and compares it
with the address of the current cycle. If the compare result proves that the read
access is on-page the read cycle is performed with wait cycles defined by
PRC.PRW[2:0].
In the page ROM configuration register (PRC), one or more of the address bits
(A3 to A6) are set as masking addresses (no comparison is made for these
addresses). The masking address is chosen according to the configuration of
the connected page ROM and the number of continuously readable bits.
Wait control for normal access (off-page) and page access (on-page) is
specified by different registers: For page access, wait control is performed
according to PRC register setting. For normal access, wait control is performed
according to DWC0 and DWC1 register settings.
The following figures show the on-page/off-page judgment during page ROM
connection for a 16-Mbit page ROM and for different data bus widths.
(1)
8-bit data bus width
The page size or the number of continuously readable bits is 32 x 8 bit. To
provide 32 addresses, a 5-bit on-page address is required. Therefore, set
PRC.MA[6:3] = 0011
B
.
Figure 7-5
16-Mbit page ROM (2 M × 8 bits), page size 32 x 8 bit
A4
A0
Internal address latch
(immediately preceding
address)
Output address
Page ROM address
Off-page address
MA6
0
MA5
0
MA4
1
MA3
1
PRC register setting
Comparison
A3
A5
A6
A7
...
...
...
A22
A4
A3
A5
A6
A7
A22
A2
A1
A2
A1
A3
A4
A5
A0
On-page address
A19
A6
A7
A21
A20
A19
A20
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