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參數(shù)資料
| 型號： | a8251 |
| 廠商： | Altera Corporation |
| 英文描述： | Programmable Communications Interface(可編程通信接口) |
| 中文描述： | 可編程通信接口（可編程通信接口） |
| 文件頁數(shù)： | 10/21頁 |
| 文件大?。?/td> | 338K |
| 代理商： | A8251 |
34
Altera Corporation
a8251 Programmable Communications Interface Data Sheet
Sync Character Two Register
The sync character two register holds the value of the second sync
character. The information is used by the receiver for sync comparison
and by the transmitter for sync character transmission.
Transmitter Buffer Register
The transmitter buffer register (TBR) holds the transmitter data, which the
a8251
formats, serializes, and transmits on the
txd
output. Once the
existing data bits in the shift register are completely transmitted, the TBR
transfers new data into the shift register.
Receiver Buffer Register
The receiver buffer register (RBR) holds the data received from the shift
register. After the shift register receives a new data word, it is ready to
transfer the new data word to the RBR. If the existing data in the RBR has
already been read by the microprocessor, then the transfer takes place. If
the existing RBR data has not been read, the overrun error (
oe
) bit is set.
Operation
This section describes the following:
I
I
I
I
Programming operation
Receiver operations: asynchronous and synchronous
Transmitter operations: asynchronous and synchronous
Reset operation
Programming Operation
The
a8251
must be programmed in a specific order and immediately
following a total state reset or an internal state reset.
First, the microprocessor writes to the MIR. When synchronous operation
is selected in the MIR, the microprocessor writes to the first sync
character. If two sync characters are selected in the MIR, the second
character is written immediately after the first; if only one sync character
is selected, the second character is skipped. However, when
asynchronous operation is selected, both sync characters are skipped.
Once the microprocessor writes to the MIR and sync characters (if
appropriate), the command instruction, status, TBR and RBR can be
randomly accessed.
Table 10
outlines the
a8251
programming sequence including the logic
level of control signals.
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