C167CS datasheet(197/517 Pages) INFINEON

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C167CS

Derivatives

The External Bus Interface

User’s Manual

9-9

V2.0, 2000-07

Disable/Enable Control for Pin BHE (BYTDIS)

Bit BYTDIS is provided for controlling the active low Byte High Enable (BHE) pin. The

function of the BHE pin is enabled, if the BYTDIS bit contains a ‘0’. Otherwise, it is

disabled and the pin can be used as standard IO pin. The BHE pin is implicitly used by

the External Bus Controller to select one of two byte-organized memory chips, which are

connected to the C167CS via a word-wide external data bus. After reset the BHE

function is automatically enabled (BYTDIS = ‘0’), if a 16-bit data bus is selected during

reset, otherwise it is disabled (BYTDIS = ‘1’). It may be disabled, if byte access to 16-bit

memory is not required, and the BHE signal is not used.

Segment Address Generation

During external accesses the EBC generates a (programmable) number of address lines

on Port 4, which extend the 16-bit address output on PORT0 or PORT1 and so increase

the accessible address space. The number of segment address lines is selected during

reset and coded in bit field SALSEL in register RP0H (see Table 9-3).

Note: The total accessible address space may be increased by accessing several banks

which are distinguished by individual chip select lines.

If Port 4 is used to output segment address lines, in most cases the drivers must

operate in push/pull mode. Make sure that OPD4 does not select open drain mode

in this case.

Table 9-3

Decoding of Segment Address Lines

SALSEL

Segment Address Lines

Directly accessible Address Space

1 1

Two:

A17 … A16

256

KByte (Default without pull-downs)

1 0

Eight: A23 … A16

MByte (Maximum)

0 1

None

KByte (Minimum)

0 0

Four:

A19 … A16

MByte

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