st92f124 STMicroelectronics, st92f124 Datasheet - Page 147

• Manufacturer Part Number: st92f124
• Description: 8/16-bit Single Voltage Flash Mcu Family With Ram, E3 Tmemulated Eeprom, Can 2.0b And J1850 Blpd
• Manufacturer: STMicroelectronics

8.3 REGISTER DESCRIPTION
EXTERNAL MEMORY REGISTER 1 (EMR1)
R245 - Read/Write
Register Page: 21
Reset value: 1000 0000 (80h)
Bit 7 = Reserved.
Bit 6 = MC: Mode Control.
0: AS, DS and RW pins have the standard ST9 for-
1: AS pin becomes ALE, Address Load Enable.
Bit 5 = DS2EN: Data Strobe 2 enable.
0: The DS pin is active for any external memory
1: If the lower memory block is addressed, the
X
7
mat.
This signal indicates to the external address
latch that a valid address is put on AD[7:0].
When ALE is high, the multiplexed address/data
bus AD[7:0] carries the LSBs of the memory ad-
dress, which must be latched on the falling edge
of this signal.
DS becomes OEN, Output ENable: When this
signal is low, the external memory should put
the data on the multiplexed address/data bus
AD[7:0]. The data is sampled by the microcon-
troller on the rising edge of the OEN signal.
RW pin becomes WEN, Write ENable: when this
signal is low, the multiplexed address/data bus
AD[7:0] carries the data to be written in the ex-
ternal memory. The external memory should
sample the data on the rising edge of the WEN
signal.
access (lower and upper memory block).
The DS2 pin remains high.
DS2 pin outputs the standard DS signal, while
the DS pin stays high during the whole memory
cycle.
MC
DS2EN
ASAF
ST92F124/F150/F250 - EXTERNAL MEMORY INTERFACE (EXTMI)
0
ETO
BSZ
X
0
Refer to
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 3 = Reserved, must be kept cleared.
Bit 2 = ETO: External toggle.
0: The external memory interface pins (AS, DS,
1: When the internal memory protection is dis-
Bit 1 = BSZ: Bus size.
0: All outputs use the standard low-noise output
1: P4[7:6], P6[5:4] use high-drive 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.
If the upper memory block is addressed, DS2 is
forced to “1” during the whole memory cycle.
DS2, RW, Port0, Port1, Port9) toggle only if an
access to external memory is performed.
abled, the above pins (except DS which never
toggles during internal memory accesses) tog-
gle during both internal and external memory
accesses.
buffers.
Figure 77
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