Home >> ATMEGA128 Search >> ATMEL Corporation ATMEGA128 Datasheet

ATMEGA128 Datasheet

8-bit Atmel Microcontroller

No Preview Available !

ATMEGA128 pdf
Address Latch
Requirements
ATmega128
The control bits for the External Memory Interface are located in three registers, the MCU Con-
trol Register – MCUCR, the External Memory Control Register A – XMCRA, and the External
Memory Control Register B – XMCRB.
When the XMEM interface is enabled, the XMEM interface will override the setting in the data
direction registers that corresponds to the ports dedicated to the XMEM interface. For details
about the port override, see the alternate functions in section “I/O Ports” on page 65. The XMEM
interface will auto-detect whether an access is internal or external. If the access is external, the
XMEM interface will output address, data, and the control signals on the ports according to Fig-
ure 13 (this figure shows the wave forms without wait-states). When ALE goes from high-to-low,
there is a valid address on AD7:0. ALE is low during a data transfer. When the XMEM interface
is enabled, also an internal access will cause activity on address, data and ALE ports, but the
RD and WR strobes will not toggle during internal access. When the External Memory Interface
is disabled, the normal pin and data direction settings are used. Note that when the XMEM inter-
face is disabled, the address space above the internal SRAM boundary is not mapped into the
internal SRAM. Figure 12 illustrates how to connect an external SRAM to the AVR using an octal
latch (typically “74 x 573” or equivalent) which is transparent when G is high.
Due to the high-speed operation of the XRAM interface, the address latch must be selected with
care for system frequencies above 8MHz @ 4V and 4MHz @ 2.7V. When operating at condi-
tions above these frequencies, the typical old style 74HC series latch becomes inadequate. The
External Memory Interface is designed in compliance to the 74AHC series latch. However, most
latches can be used as long they comply with the main timing parameters. The main parameters
for the address latch are:
• D to Q propagation delay (tPD).
• Data setup time before G low (tSU).
• Data (address) hold time after G low (TH).
The External Memory Interface is designed to guaranty minimum address hold time after G is
asserted low of th = 5 ns. Refer to tLAXX_LD/tLLAXX_ST in “External Data Memory Timing” Tables
137 through Tables 144 on pages 328 - 330. The D-to-Q propagation delay (tPD) must be taken
into consideration when calculating the access time requirement of the external component. The
data setup time before G low (tSU) must not exceed address valid to ALE low (tAVLLC) minus PCB
wiring delay (dependent on the capacitive load).
Figure 12. External SRAM Connected to the AVR
AD7:0
ALE
AVR
A15:8
RD
WR
DQ
G
D[7:0]
A[7:0]
SRAM
A[15:8]
RD
WR
2467X–AVR–06/11
27
ATMEL Corporation
ATMEL Corporation


PDF Click to Download PDF File

PDF View for Mobile



Related Start with ATMEGA12*

[ ATMEGA128 ATMEL Corporation ]     [ ATMEGA1280 ATMEL Corporation ]     [ ATMEGA1280V ATMEL ]     [ ATMEGA1281 ATMEL Corporation ]     [ ATMEGA1281V ATMEL ]     [ ATMEGA1284 ATMEL Corporation ]     [ ATMEGA1284 ATMEL ]     [ ATMEGA1284P ATMEL Corporation ]     [ ATMEGA1284P ATMEL ]     [ ATMEGA1284RFR2 ATMEL ]     [ ATMEGA128A ATMEL Corporation ]     [ ATMEGA128L ATMEL Corporation ]     [ ATMEGA128RFA1 Atmel Corporation ]     [ ATMEGA128RFR2 ATMEL ]     [ ATMEGA103 ATMEL Corporation ]     [ ATMEGA103L ATMEL Corporation ]     [ ATMEGA128 ATMEL Corporation ]     [ ATMEGA1280 ATMEL Corporation ]     [ ATMEGA1280V ATMEL ]     [ ATMEGA1281 ATMEL Corporation ]     [ ATMEGA1281V ATMEL ]     [ ATMEGA1284 ATMEL Corporation ]     [ ATMEGA1284 ATMEL ]     [ ATMEGA1284P ATMEL Corporation ]    


Searches related to ATMEGA128 part

Find Chips CBC RS online RUTRONIK 24
Component Distributors NexGen Digital Richardson RFPD ICC
Beyond Components NAC PEI-Genesis Powell Electronics
TME Ameya 360 Power & Signal Datasheets360
Freelance Electronics Sager Electronics Terminals & Connectors TTI

0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z
@ 2014 :: DatasheetsPDF.com :: Semiconductors Datasheet Search & Download Site