ST16C550(2003) データシートの表示（PDF） - Exar Corporation
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ST16C550 Datasheet PDF : 35 Pages
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ST16C550
SYMBOL DESCRIPTION
Symbol
-IOR
-IOW
INT
-RXRDY
-TXRDY
-BAUDOUT
Pin
Signal
40 44 48 type
Pin Description
21 24 19
I Read data strobe (active low strobe). A logic 0 on this pin
transfers the contents of the ST16C550 data bus to the CPU.
Connect to logic 1 when using IOR.
18 20 16
I Write data strobe (active low strobe). A logic 0 on this pin
transfers the contents of the CPU data bus to the addressed
internal register. Connect to logic 1 when using IOW.
30 33 30
O Interrupt Request (active high). Interrupts are enabled in the
interrupt enable register (IER), and when an interrupt con-
dition exists. Interrupt conditions include: receiver errors,
available receiver buffer data, transmit buffer empty, or
when a modem status flag is detected.
29
32
29
O Receive Ready. When operating in the FIFO mode, one of
two types of DMA signaling can be selected using the FIFO
control register bit-3. When operating in the ST16C450
mode, only DMA mode “0” is allowed. Mode “0” supports
single transfer DMA in which a transfer is made between
CPU bus cycles. Mode “1” supports multi-transfer DMA in
which multiple transfers are made continuously until the
receiver FIFO has been emptied. In DMA mode “0” -RXRDY
is low, when there is at least one character in the receiver
FIFO or receive holding register. In DMA mode “1”, -RXRDY
is low, when the trigger level or the time-out has been
reached.
24
27
23
O Transmit Ready. When operating in the FIFO mode, one of
two types of DMA signaling can be selected using the FIFO
control register bit-3. When operating in the ST16C450
mode, only DMA mode “0” is allowed. Mode “0” supports
single transfer DMA in which a transfer is made between
CPU bus cycles. Mode “1” supports multi-transfer DMA in
which multiple transfers are made continuously until the
transmit FIFO has been filled.
15
17
12
O Baud Rate Generator Output. This pin provides the 16X
clock of the selected data rate from the baud rate generator.
The RCLK pin must be connected externally to -BAUDOUT
when the receiver is operating at the same data rate.
Rev. 4.30
5
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