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Programmer’s Reference
4-20
Copyright © ARM Limited 2000. All rights reserved.
4.4
Programming the keyboard controller
The SA-1100 and the keyboard controller communicate using the SPI bus, which
utilizes a number of GPIO pins provided by the SA-1100. The operation of the keyboard
controller is controlled by accessing internal registers, of which it contains two banks
of 255 registers. These are accessed using a message exchange protocol. The timing for
the SPI bus is described in Keyboard controller host interface timing on page 4-23.
4.4.1
Message structure
The SA-1100 uses messages to read from and write to individual bits within the internal
registers. Messages are also used by the keyboard controller to report events and to
respond to reads and writes by the host. Each message comprises:
•
a header
•
a command or a report identifier
•
a message body, if necessary
•
a Longitudinal Redundancy Check (LRC)
The header identifies the message type and is followed by a byte containing a command
code or register offset. The message body contains any data to be written or read from
a register. The LRC byte is used to verify the packet data. The read/write/report
message blocks contains a message length descriptor and between 1 and 32 bytes of
data.
Figure 4-1 shows the general structure of messages.
Figure 4-1 Keyboard controller message structure
Protocol header
Message/report identifier
LRC
Message body
(if required)
Содержание Prospector P1100
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Страница 140: ...Connector reference A 18 Copyright ARM Limited 2000 All rights reserved ARM DUI 0122A ...