ST92F120 datasheet(115/324 Pages) STMICROELECTRONICS

115 / 324 page

115/324

ST92F120 - EXTERNAL MEMORY INTERFACE (EXTMI)

8.3 REGISTER DESCRIPTION

EXTERNAL MEMORY REGISTER 1 (EMR1)

R245 - Read/Write

Reset value: 1000 0000 (80h)

Bit 7 = Reserved.

Bit 6 = MC:

Mode Control.

0: AS, DS and RW pins have the standard ST9

meaning.

1: AS pin becomes ALE, Address Load Enable

(AS inverted); Thus Memory Adress, Read/

Write signals are valid whenever a falling edge

of ALE occurs.

DS becomes OEN, Output ENable: it has the

standard ST9 meaning during external read op-

erations, but is forced to “1” during external write

operations.

RW pin becomes WEN, Write ENable: it follows

the standard ST9 DS meaning during external

write operations, but is forced to “1” during ex-

ternal read operations.

Bit 5 = DS2EN:

Data Strobe 2 enable.

0: The DS2 pin is forced to “1” during the whole

memory cycle. In this case, access to upper or

lower memory is controlled by the DS pin.

1: If the lower memory block is addressed, the

DS2 pin follows the standard ST9 DS meaning

(if MC=0) or it becomes OEN (if MC=1). The DS

pin is forced to 1 during the whole memory cy-

cle.

If the upper memory block is used, DS2 is forced

to “1” during the whole memory cycle. The DS

pin behaviour is not modified.

Refer to Figure 57

Bit 4 = ASAF:

Address Strobe as Alternate Func-

tion.

Depending on the device, AS can be either a ded-

icated pin or a port Alternate Function. This bit is

used only in the second case.

0: AS Alternate function disabled.

1: AS Alternate Function enabled.

Bit 2 = ETO:

External toggle.

0: The external memory interface pins (AS, DS,

DS2, RW, Port0, Port1) toggle only if an access

to external memory is performed.

1: When the internal memory protection is dis-

abled (mask option available on some devices

only), the above pins (except DS and DS2 which

never toggle during internal memory accesses)

toggle during both internal and external memory

accesses.

Bit 1 = BSZ:

Bus size.

0: All the I/O ports including the external memory

interface pins use smaller, less noisy output

buffers. This may limit the operation frequency

of the device, unless the clock is slow enough or

sufficient wait states are inserted.

1: All the I/O ports including the external memory

interface pins (AS, DS, DS2, R/W, Port 0, 1) use

larger, more noisy output buffers .

Bit 0 = Reserved.

CAUTION: External memory must be correctly ad-

dressed before and after a write operation on the

EMR1 register. For example, if code is fetched

from external memory using the standard ST9 ex-

ternal memory interface configuration (MC=0),

setting the MC bit will cause the device to behave

unpredictably.

DS2EN

ASAF

ETO

BSZ

ST92F120 датащи(PDF) 115 Page - STMicroelectronics

ST92F120 датащи(HTML) 115 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL