CY7C67300
Document #: 38-08015 Rev. *J Page 5 of 99
External Memory Interface
EZ-Host provides a robust interface to a wide variety of external
memory arrays. All available external memory array locations
can contain either code or data. The CY16 RISC processor
directly addresses a flat memory space from 0x0000 to 0xFFFF.
External Memory Interface Features
■Supports 8-bit or 16-bit SRAM or ROM
■SRAM or ROM can be used for code or data space
■Direct addressing of SRAM or ROM
■Two external memory mapped page registers
External Memory Access Strobes
Access to external memory is sampled asynchronously on the
rising edge of strobes with a minimum of one wait state cycle. Up
to seven wait state cycles may be inserted for external memory
access. Each additional wait state cycle stretches the external
memory access time by 21 ns (you must be running in internal
memory when changing wait states). An external memory device
with 12 ns access time is necessary to support 48 MHz code
execution.
Page Registers
EZ-Host allows extended data or program code to be stored in
external SRAM, or ROM. The total size of extended memory can
be up to 512K bytes. The CY16 processor can access extended
memory via two address regions of 0x8000-0x9FFF and
0xA000-0xBFFF. The page register 0xC018 can be used to
control the address region 0x8000-0x9FFF and the page register
0xC01A controls the address region of 0xA000-0xBFFF.
Figure1 illu strates that when the nXMEMSEL pin is asserted the
upper CPU address pins are driven by the contents of the Page
x registers.
Merge Mode
Merge modes enabled through the External Memory Control
register [0xC03A] allow combining of external memory regions in
accordance with the following:
■nXMEMSEL is active from 0x8000 to 0xBFFF
■nXRAMSEL is active from 0x4000 to 0x7FFF when RAM Merge
is disabled; nXRAMSEL is active from 0x4000 to 0xBFFF when
RAM Merge is enabled
■nXROMSEL is active from 0xC100 to 0xDFFF when ROM
Merge is disabled; nXROMSEL is active from 0x8000 to
0xDFFF (excluding the 0xC000 to 0xC0FF area) when ROM
Merge is enabled
Program Memory Hole Description
Code residing in the 0xC000-0xC0FF address space is not
accessible by the CPU.
DMA to External Memory Prohibited
EZ-Host supports an internal DMA engine to rapidly move data
between different functional blocks within the chip. This DMA
engine is used for SIE1, SIE2, HPI, SPI, HSS, and IDE but it can
only transfer data between the specified block and internal RAM
or ROM. Setting up the DMA engine to transfer to or from an
external memory space might result in internal RAM data
corruption because the hardware (for example,
HSS/HPI/SIE1/SIE2/IDE) does not explicitly check the address
range. For example, setting up a DMA transfer to external
address 0x8000 might result in a DMA transfer into address
0x0000.
External Memory Related Resource Considerations:
■By default A[18:15] are not available for general addressing
and are driven high on power up. The Upper Address Enable
register must be written appropriately to enable A[18:15] for
general addressing purposes.
■47K ohm external pull up on pin A15 for 12 MHz crystal
operation.
■During the 3 ms BIOS boot procedure the CPU external
memory bus is active.
■ROM boot load value 0xC3B6 located at 0xC100.
■HPI, HSS, SPI, SIE1, SIE2, and IDE cannot DMA to external
memory arrays.
■Page 1 banking is always enabled and is in effect from 0x8000
to 0x9FFF.
■Page 2 banking is always enabled and is in effect from 0xA000
to 0xBFFF.
■CPU memory bus strobes may wiggle when chip selects are
inactive.
Figure 1. Page n Registers External Address Pins Logic
0000 + PC[14:0] 1
0
PAGEx Register[5:0] + PC[12:0]
nXMEMSEL Pin
A[18:0]
PC = Program Counter
x = 1 or 2
A = CPU Address Bus
Where:
PAGE 1 Register Active Range = 8000h to 9FFFh
PAGE 2 Register Active Range = A000h to BFFFh
Note:
nXMEMSEL Pin Active Range = 8000h to BFFFh
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