MEC1322 datasheet(118/456 Pages) MICROCHIP

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MEC1322

DS00001719D-page 118

 2014 - 2015 Microchip Technology Inc.

9.8.2

EC DATA REGISTER

The 4 1-byte EC Data Byte registers function as a 32-bit register, which creates a 4 byte window into the Memory

REGION being accessed. The 4-byte window is always aligned on a 4-byte boundary. Depending on the read/write con-

figuration of the memory region being accessed, the bytes may be extracted from or loaded into memory as a byte,

word, or a DWord. The ACCESS_TYPE determines the size of the memory access. The address accessed is deter-

mined by the two EC_Address byte registers, which together function as a 15-bit EC Address Register.

• A write to the EC Data Register when the EC Address is in a read-only or a no-access region, as defined by the

Memory Base and Limit registers, will update the EC Data Register but memory will not be modified.

• A read to the EC Data Register when the EC Address is in a no-access region, as defined by the Memory Base

and Limit registers, will not trigger a memory read and will not modify the EC Data Register. In auto-increment

mode (ACCESS_TYPE=11b), reads of Byte 3 of the EC Data Register will still trigger increments of the EC

Address Register when the address is out of bounds, while writes of Byte 3 will not.

9.8.3

ACCESS TYPES

The access type field (ACCESS_TYPE in the EC Address LSB Register) defines the type of host access that occurs

when the EC Data Register is read or written.

11:

Auto-increment 32-bit access. This defines a 32-bit access, as in the 10 case. In addition, any read or write of

Byte 3 in the EC Data Register causes the EC Data Register to be incremented by 1. That is, the EC_Address

field will point to the next 32-bit double word in the 32- bit internal address space.

10:

32-bit access. A read of Byte 0 in the EC Data Register causes the 32 bits in the 32- bit internal address space

at an offset of EC_Address to be loaded into the entire EC Data Register. The read then returns the contents of

Byte 0. A read of Byte 1, Byte 2 or Byte 3 in the EC Data Register returns the contents of the register, without

any update from the 32- bit internal address space.

A write of Byte 3 in the EC Data Register causes the EC Data Register to be written into the 32 bits in the 32- bit

internal address space at an offset of EC_Address. A write of Byte 0, Byte 1 or Byte 2 in the EC Data Register

updates the contents of the register, without any change to the 32- bit internal address space.

01:

16-bit access. A read of Byte 0 in the EC Data Register causes the 16 bits in the 32- bit internal address space

at an offset of EC_Address to be loaded into Byte 0 and Byte 1 of the EC Data Register. The read then returns

the contents of Byte 0. A read of Byte 2 in the EC Data Register causes the 16 bits in the 32- bit internal address

space at an offset of EC_Address+2 to be loaded into Byte 2 and Byte 3 of the EC Data Register. The read then

returns the contents of Byte 2. A read of Byte 1 or Byte 3 in the EC Data Register return the contents of the reg-

ister, without any update from the 32- bit internal address space.

A write of Byte 1 in the EC Data Register causes Bytes 1 and 0 of the EC Data Register to be written into the 16

bits in the 32- bit internal address space at an offset of EC_Address. A write of Byte 3 in the EC Data Register

causes Bytes 3 and 2 of the EC Data Register to be written into the 16 bits in the 32- bit internal address space

at an offset of EC_Address+2. A write of Byte 0 or Byte 2 in the EC Data Register updates the contents of the

00:

8-bit access. Any byte read of Byte 0 through Byte 3 in the EC Data Register causes the corresponding byte

within the 32-bit double word addressed by EC_Address to be loaded into the byte of EC Data Register and

returned by the read. Any byte write to Byte 0 through Byte 3 in the EC Data Register writes the corresponding

byte within the 32-bit double word addressed by EC_Address, as well as the byte of the EC Data Register.

9.8.4

EMBEDDED MEMORY INTERFACE USAGE

The Embedded Memory Interface provides a generic facility for communication between the Host and the EC and can

be used for many functions. Some examples are:

• Virtual registers. A block of memory in the 32-bit internal address space can be used to implement a set of virtual

registers. The Host is given direct read-only access to this address space, referred to as peek mode. The EC may

read or write this memory as needed.

• Program downloading. Because the Instruction Closely Coupled Memory is implemented in the same 32-bit inter-

nal address space, the Embedded Memory Interface can be used by the Host to download new program seg-

ments for the EC in the upper 32KB SRAM. The Read/Write window would be configured by the Host to point to

the beginning of the loadable program region, which could then be loaded by the Host.

• Data exchange. The Read/Write portion of the memory window can be used to contain a communication packet.

The Host, by default, “owns” the packet, and can write it at any time. When the Host wishes to communicate with

the EC, it sends the EC a command, through the Host-to-EC message facility, to read the packet and perform

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