Memory Controller

Table 6-37. 8-Bit I/O Space Write Commands (nIOIS16 = 1)

nPCE2

nPCE1

MA<0>

nPIOR

nPIOW

MD[15:8]

MD[7:0]

 

 

 

 

 

 

 

1

0

0

1

0

Unimportant

Even Byte

 

 

 

 

 

 

 

1

0

1

1

0

Unimportant

Odd Byte

 

 

 

 

 

 

 

Table 6-38. 8-Bit I/O Space Read Commands (nIOIS16 = 1)

nPCE2

nPCE1

MA<0>

nPIOR

nPIOW

MD[15:8]

MD[7:0]

 

 

 

 

 

 

 

1

0

0

0

1

Unimportant

Even Byte

 

 

 

 

 

 

 

1

0

1

0

1

Unimportant

Odd Byte

 

 

 

 

 

 

 

6.8.4External Logic for 16-Bit PC Card Implementation

The PXA255 processor requires external glue logic to complete the 16-bit PC Card socket interface that allows either 1-socket or 2-socket solutions.

Figure 6-27and Figure 6-28show general solutions for a one- and two-socket configuration. The pull-ups shown are included as specified in the PC Card Standard - Volume 2 - Electrical Specification. Low-power systems must remove power from the pull-ups during sleep to avoid unnecessary power consumption.

GPIO or memory-mapped external registers can be used to control the reset of the 16-bit PC Card interface, power selection (VCC and VPP), and drive enables. The INPACK# signal is not used.

Figure 6-27and Figure 6-28provide the logical connections necessary to support hot insertion capability. For dual-voltage support, level shifting buffers are required for all PXA255 processor input signals. Hot insertion capability requires that each socket be electrically isolated from the other and from the remainder of the memory system. If one or both of these features is not required, then some of the logic shown in the following diagrams can be eliminated.

Software is responsible for setting the MECR[NOS] and MECR[CIT] bits. NOS indicates the number of sockets that the system support while CIT is written when the Card is in place. Input pins nPWAIT and nIOIS16 are three stated until card detect (CD) signal is asserted. To achieve this, software programs the MECR[CIT] bit when a card is detected. If the MECR[CIT] is 0, the nPWAIT and nIOIS16 inputs are ignored.

Figure 6-27shows the minimal glue logic needed for a 1-socket system, including: data transceivers, address buffers, and level shifting buffers. The transceivers are enabled by the PSKTSEL signal. The DIR pin of the transceiver is driven by the RD/nWR pin. A GPIO is used for the three-state signal of the address and nPWE lines. These signals must be three-stated because they are used for memories other than the card interface. The Card Detect[1:0] signals are driven by the signal device.

6-66

Intel® PXA255 Processor Developer’s Manual

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Intel PXA255 manual External Logic for 16-Bit PC Card Implementation, Bit I/O Space Write Commands nIOIS16 =