PXB4340E Datasheet, PDF (47/185 Pages) Infineon Technologies AG – ICs for Communications

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The microprocessor can not access these RAMs directly, but uses a transfer register set. It
consists of three blocks:
• read register block
• write register block
• mask register block.
In addition an address register specifying the entry to be accessed and a command register to
specify the RAM and to start the transfer are defined. The PXB 4340 AOP uses one single
access type, the read-modify-write transfer, where the old data is transferred from the specified
RAM entry to the Read Transfer Registers and the contents of the Write Transfer Registers are
written to the RAM entry for those bits which are unmasked.
In addition to the read-modify-write access executed upon microprocessor command for a single
entry, there are two other access types to the external RAM (figure 30):
• the access initiated by the passing ATM cell
• the SCAN access for OAM and/or DMA.
internal or external RAM
RAM entry n
select
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Mask
Registers
RAM entry k
write ^M
U
X
Write Transfer
Registers
read
Data
RAM entry 0
Read Transfer
Registers
—3
Address
transfer
command
Address = k
CMR Register
Address Register
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Data Sheet
2-47
04.2000