CS89712 datasheet(93/170 Pages) CIRRUS

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CS89712

DS502PP2

3.7.2

MEMCFG2 Memory Configuration Register 2 (address 0x8000.01C0)

The Memory Configuration Register 2 is a 32-bit read / write register which sets the configuration of the two expan-

sion and ROM selects nCS[4:5]. Each select is configured with a 1-byte field starting with expansion select 4.

Each of the six non-reserved byte fields for chip select configuration in the memory configuration registers are iden-

tical and define the number of wait states, the bus width, enable EXPCLK output during accesses and enable se-

quential mode access. This byte field is defined below. This arrangement applies to nCS[0:3], and nCS[4:5] when

the PC CARD enable bits in the SYSCON2 register are not set. The state of these bits is ignored for the Boot ROM

and local SRAM fields in the MEMCFG2 register.

Table 45 defines the bus width field. Note that the effect of this field is dependent on the two BOOTBIT bits that can

be read in the SYSFLG1 register. All bits in the memory configuration register are cleared by a system reset, and

the state of the BOOTBIT bits are determined by Port E bits 0 and 1 on the CS89712 during power-on reset. The

state of PE[1] and PE[0] determine whether the CS89712 is going to boot from either 32-bit-wide, 16-bit-wide or 8-

bit-wide ROMs.

Table 46 shows the values for the wait states for random and sequential wait states at 18 MHz bus. At 36 MHz bus

rate, the encoding becomes more complex. Table 47 preserves compatibility with the previous devices, while allow-

ing the previously unused bit combinations to specify more variations of random and sequential wait states.

Note: See

AC Characteristics for more detail on bus timing.

The memory area decoded by CS[6] is reserved for the on-chip SRAM, hence this does not require a configuration

field in MEMCFG2. It is automatically set up for 32-bit-wide, no-wait-state accesses. For the Boot ROM, it is auto-

matically set up for 8-bit, no wait state accesses.

Chip selects nCS[4] and nCS[5] are used to select two CL-PS6700 PC CARD controller devices. These have a mul-

tiplexed 16-bit wide address / data interface, and the configuration bytes in the MEMCFG2 register have no meaning

when these interfaces are enabled.

31:24

23:16

15:8

7:0

(Boot ROM)

(Local SRAM)

nCS[5] configuration

nCS[4] configuration

5:2

1:0

CLKENB

SQAEN

Wait States Field

Bus width

Bus Width Field

BOOTBIT1

BOOTBIT0

Expansion Transfer Mode

Port E bits 1,0 during

NPOR reset

32-bit wide bus access

Low, Low

16-bit wide bus access

Low, Low

8-bit wide bus access

Low, Low

Reserved

Low, Low

8-bit wide bus access

Low, High

Reserved

Low, High

32-bit wide bus access

Low, High

16-bit wide bus access

Low, High

16-bit wide bus access

High, Low

32-bit wide bus access

High, Low

Reserved

High, Low

8-bit wide bus access

High, Low

Table 45. Values of the Bus Width Field

CS89712 Datasheet(PDF) 93 Page - Cirrus Logic

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