Specifications

3706C–MICRO–2/11

AT89LP3240/6440

3.3.4 External Memory Interface

The AT89LP3240/6440 uses the standard 8051 external memory interface with the upper

address on Port 2, the lower address and data in/out multiplexed on Port 0, and the ALE, RD

and WR strobes. The interface may be used in two different configurations depending on which

type of MOVX instruction is used to access XDATA.

Figure 3-7 shows a hardware configuration for accessing up to 64K bytes of external RAM using

a 16-bit linear address. Port 0 serves as a multiplexed address/data bus to the RAM. The

Address Latch En

able strobe (ALE) is used to latch the lower address byte into an external reg-

ister so that Port 0 can be freed for data input/output. Port 2 provides the upper address byte

throughou t the operation. The MOVX @DPTR instructions use Linear Address mode

Figure 3-7. External Memory 16-bit Linear Address Mode

Table 3-3.

MEMCON – Memory Control Register

MEMCON = 96H Reset Value = 0000 00XXB

Not Bit Addressable

IAP AERS LDPG MWEN DMEN ERR – WRTINH

Bit76543210

Symbol Function

IAP In-Application Programming Enable. When IAP = 1 and the IAP Fuse is enabled, programming of the CODE/SIG space

is enabled and MOVX @DPTR instructions will access CODE/SIG instead of EDATA or FDATA. Clear IAP to disable

programming of CODE/SIG and allow access to EDATA and FDATA.

AERS Auto-Erase Enable. Set to perform an auto-erase of a Flash memory page (CODE, SIG or FDATA) during the next write

sequence. Clear to perform write withou

t erase.

LDPG Load Page Enable. Set to this bit to load multiple bytes to the temporary page buffer. Byte locations may not be loaded

more than once before a write. LDPG must be cleared before writing.

MWEN Memory Write Enable. Set to enable programming of a nonvolatile memory location (CODE, SIG or FDATA). Clear to

disable programming of all nonvolatile memories.

DMEN Data Memory Enable. Set to enable nonvolatile data

memory and map it into the FDATA space. Clear to disable

nonvolatile data memory.

ERR Error Flag. Set by hardware if an error occurred during the last programming sequence due to a brownout condition (low

voltage on VDD). Must be cleared by software.

WRTINH Write Inhibit Flag. Cleared by hardware when the voltage on VDD has fallen below the minimum programming voltage.

Set by hardware when the voltage on VDD is above the minimum programming voltage.

ALE

AT89LP

DATA

LATCH

EXTERNAL

DATA

MEMORY

ADDR