TMPR4938 datasheet(132/716 Pages) TOSHIBA

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Chapter 7 External Bus Controller

7-22

(2) 16-bit ISA module

Following is a programming example to use a 16-bit ISA module:

•

ISA mode (EBCCRn.ISA=01)

•

16-bit bus (EBCCRn.BSZ=10)

•

READY mode (EBCCRn.RDY=1, EBCCRn.PM=00)

•

Channel enable (EBCCRn.ME=1)

•

ISA select (PCFG.ISA_SEL=1)

Program the number of wait cycles, the SHWT option and the bus speed according to the ISA

module used. Figure 7.3.17 shows an example of connecting a 16-bit ISA module to the TX4938.

Figure 7.3.17 An Example of Connecting an 16-Bit ISA Module

With the EBUSC configured for a 16-bit bus, bits [16:1] of physical addresses are driven out

from ADDR[15:0]. Thus, the address pins must be connected, as shown in Figure 7.3.17. To

access halfwords in the ISA module with even addresses (*0, *2, *4, *6, …), the TX4938 must

provide physical addresses with two low-order bits cleared (*0, *4, *8, *C, …). Therefore, the

accessible ISA address space is limited to a maximum of 32 kbytes between 0x0000 and 0x7fff.

For byte accesses, the valid byte lane in the data bus differs, depending on whether the TX4938

is configured for big-endian or little-endian byte ordering. Software is responsible for address

conversion for a specific endianness, as shown in Table 7.3.8.

TX4938

ADDR[15:0]

DATA[15:0]

IOR*

IOW*

ACK*/READY

ISA-Module

SA[15:0]

SD[15:0]

IOR*

IOW*

IOCHRDY

AEN

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