ST92T163 ST Microelectronics, ST92T163 Datasheet - Page 97

• Manufacturer Part Number: ST92T163
• Description: 8/16-BIT FULL SPEED USB MCU FOR COMPOSITE DEVICES WITH 16 ENDPOINTS
• Manufacturer: ST Microelectronics

REGISTER DESCRIPTION (Cont’d)
Bit 1:0 = UAS[1:0]: Upper memory address strobe
stretch .
These two bits contain the number of wait cycles
(from 0 to 3) to add to the System Clock to stretch
AS during external upper memory block accesses
(MSB of 22-bit internal address=1). The reset val-
ue is 3.
WARNING: The EMR2 register cannot be written
during an interrupt service routine.
WAIT CONTROL REGISTER (WCR)
R252 - Read/Write
Register Page: 0
Reset Value: 0111 1111 (7Fh)
Bit 7 = Reserved, forced by hardware to 0.
Bit 6 = WDGEN: Watchdog Enable.
For a description of this bit, refer to the Timer/
Watchdog chapter.
WARNING: Clearing this bit has the effect of set-
ting the Timer/Watchdog to Watchdog mode. Un-
less this is desired, it must be set to “1”.
Bit 5:3 = UDS[2:0]: Upper memory data strobe
stretch.
These bits contain the number of INTCLK cycles
to be added automatically to DS for external upper
memory block accesses. UDS = 0 adds no addi-
7
0
WDGEN UDS2
UDS1
UDS0
LDS2
LDS1
ST92163 - EXTERNAL MEMORY INTERFACE (EXTMI)
LDS0
0
tional wait cycles. UDS = 7 adds the maximum 7
INTCLK cycles (reset condition).
Bit 2:0 = LDS[2:0]: Lower memory data strobe
stretch.
These bits contain the number of INTCLK cycles
to be added automatically to DS or DS2 (depend-
ing on the DS2EN bit of the EMR1 register) for ex-
ternal lower memory block accesses. LDS = 0
adds no additional wait cycles, LDS = 7 adds the
maximum 7 INTCLK cycles (reset condition).
Note 1: The number of clock cycles added refers
to INTCLK and NOT to CPUCLK.
Note 2: The distinction between the Upper memo-
ry block and the Lower memory block allows differ-
ent wait cycles between the first 2 Mbytes and the
second 2 Mbytes, and allows 2 different data
strobe signals to be used to access 2 different
memories.
Typically, the RAM will be located above address
0x200000
0x1FFFFF, with different access times. No extra
hardware is required as DS is used to access the
upper memory block and DS2 is used to access
the lower memory block.
WARNING: The reset value of the Wait Control
Register gives the maximum number of Wait cy-
cles for external memory. To get optimum perfor-
mance from the ST9, the user should write the
UDS[2:0] and LDS[2:0] bits to 0, if the external ad-
dressed memories are fast enough.
and
the
ROM
below
address
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