
External Bus Interface (EBI)
MPC5644A Microcontroller Reference Manual, Rev. 6
334
Freescale Semiconductor
14.6.3
Running with asynchronous memories
The EBI also supports asychronous memories. In this case, the CLKOUT, TS, and BDIP pins are not used
by the memory and bursting is not supported. However, the EBI still drives these outputs, and always
drives and latches all signals at posedge CLKOUT (i.e., there is no “asynchronous mode” for the EBI).
The data timing is controlled by setting the SCY bits in the appropriate Option Register to the proper
number of wait states to work with the access time of the asynchronous memory, just as done for a
synchronous memory.
14.6.3.1
Example wait state calculation
This example applies to any chip-select memory, synchronous or asynchronous.
As an example, say we have a memory with 50ns access time, and we are running the external bus at
66 MHz (CLKOUT period: 15.2 ns). Assume the input data spec for the MCU is 4 ns.
number of wait states = (access time) / (CLKOUT period) + (0 or 1) (depending on setup time)
50/15.2 = 3 with 4.4 ns remaining (so we need at least 3 wait states, now check setup time)
15.2-4.4=10.8 ns (this is the achieved input data setup time)
Since actual input setup (10.8 ns) is greater than the input setup spec (4.0ns), 3 wait states is sufficient. If
the actual input setup was less than 4.0ns, we would have to use 4 wait states instead.
14.6.3.2
Timing and connections for asynchronous memories
The connections to an asynchronous memory are the same as for a synchronous memory, except that the
CLKOUT, TS, and BDIP signals are not used.
shows a block diagram of an MCU connected
to an asynchronous memory.
Figure 14-39. MCU Connected to Asynchronous Memory
shows a timing diagram of a read operation to a 16-bit asynchronous memory using 3 wait
states.
ADDR[9:30]
A[0:21]
Asynchronous
CE
CS0
Memory
DATA[0:15]
D[0:15]
WE*
OE
OE
MCU
WE0/BE0
* Flash memories typically use one WE signal as shown, RAMs use 2 or 4 (16-bit or 32-bit)
Содержание MPC5644A
Страница 2: ...MPC5644A Microcontroller Reference Manual Rev 6 2 Freescale Semiconductor...
Страница 24: ...MPC5644A Microcontroller Reference Manual Rev 6 24 Freescale Semiconductor...
Страница 26: ...MPC5644A Microcontroller Reference Manual Rev 6 26 Freescale Semiconductor...
Страница 52: ...Introduction MPC5644A Microcontroller Reference Manual Rev 6 52 Freescale Semiconductor...
Страница 56: ...Memory Map MPC5644A Microcontroller Reference Manual Rev 6 56 Freescale Semiconductor...
Страница 130: ...Device Performance Optimization MPC5644A Microcontroller Reference Manual Rev 6 130 Freescale Semiconductor...
Страница 204: ...Multi Layer AHB Crossbar Switch XBAR MPC5644A Microcontroller Reference Manual Rev 6 204 Freescale Semiconductor...
Страница 212: ...Peripheral Bridge PBRIDGE MPC5644A Microcontroller Reference Manual Rev 6 212 Freescale Semiconductor...
Страница 558: ...System Integration Unit SIU MPC5644A Microcontroller Reference Manual Rev 6 558 Freescale Semiconductor...
Страница 582: ...Frequency modulated phase locked loop FMPLL MPC5644A Microcontroller Reference Manual Rev 6 582 Freescale Semiconductor...
Страница 766: ...Enhanced Time Processing Unit eTPU2 MPC5644A Microcontroller Reference Manual Rev 6 766 Freescale Semiconductor...
Страница 1228: ...Decimation Filter MPC5644A Microcontroller Reference Manual Rev 6 1228 Freescale Semiconductor...
Страница 1236: ...System Information Module and Trim SIM MPC5644A Microcontroller Reference Manual Rev 6 1236 Freescale Semiconductor...
Страница 1250: ...Cyclic Redundancy Checker CRC Unit MPC5644A Microcontroller Reference Manual Rev 6 1250 Freescale Semiconductor...
Страница 1336: ...Deserial Serial Peripheral Interface DSPI MPC5644A Microcontroller Reference Manual Rev 6 1336 Freescale Semiconductor...
Страница 1388: ...Enhanced Serial Communication Interface ESCI MPC5644A Microcontroller Reference Manual Rev 6 1388 Freescale Semiconductor...
Страница 1440: ...FlexCAN Module MPC5644A Microcontroller Reference Manual Rev 6 1440 Freescale Semiconductor...
Страница 1624: ...FlexRay Communication Controller FlexRay MPC5644A Microcontroller Reference Manual Rev 6 1624 Freescale Semiconductor...
Страница 1670: ...JTAG Controller JTAGC MPC5644A Microcontroller Reference Manual Rev 6 1670 Freescale Semiconductor...
Страница 1692: ...Nexus Port Controller NPC MPC5644A Microcontroller Reference Manual Rev 6 1692 Freescale Semiconductor...
Страница 1701: ...Development Trigger Semaphore DTS MPC5644A Microcontroller Reference Manual Rev 6 Freescale Semiconductor 1701...
Страница 1702: ...Development Trigger Semaphore DTS MPC5644A Microcontroller Reference Manual Rev 6 1702 Freescale Semiconductor...