
ST20-GP1
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PlinkEmi register
The
PlinkEmi
register determines the mode of operation of the port.
PlinkIO
The
PlinkIO
register determines the direction of the port interactions when in the DMA mode of
operation.
PlinkMode
The
PlinkMode
register determines the external protocol used for interactions.
15.4 External data transfer protocols
The byte-wide parallel port has three control pins.
PlinknotReq
and
control data
transfers and the
PlinkOut
pin controls external buffers, if required (e.g. an external 3V/5V buffer
device). When the
PlinkOut
pin is high it signals the plink is outputting.
The control pins can support three external protocols, as follows:
Dreq/Dack protocol
Valid/Ack protocol
Direct DMA protocol
The protocol used for interactions is programmable via the
PlinkMode
register. In addition, the
direction of the link is controlled by the
PlinkIO
register (see Table 15.2).
PlinkEmi
Parallel port base address + #00
Read/Write
Bit
Bit field
Function
This bit determines the mode of operation of the port.
PlinkEmi
Mode
0
DMA mode (reset state)
1
EMI mode
Table 15.1
PlinkEmi
register format
0
PlinkEmi
PlinkIO
Parallel port base address + #04
Read/Write
Bit
Bit field
Function
This bit controls the direction of the parallel port interactions when in DMA mode.
PlinkIO
Direction
0
inputs (reset state)
1
outputs
Table 15.2
PlinkIO
register format
0
PlinkIO
PlinkMode
Parallel port base address + #08
Read/Write
Bit
Bit field
Function
These bits control the external protocol used for interactions.
PlinkMode
Protocol
00
Idle (reset state)
01
Dreq/Dack mode
10
Valid/Ack mode
11
Direct mode
Table 15.3
PlinkMode
register format
0
PlinkMode