82C50A Datasheet, PDF (3/21 Pages) Intersil Corporation – CMOS Asynchronous Communications Element

82C50A
Pin Description
PIN
SYMBOL NUMBER
DISTR,
22
DISTR
21
TYPE
I
I
DOSTR,
19
I
DOSTR
18
I
D0-D7
1-8
I/O
A0, A1,
28, 27,
I
A2
26
I
XTAL1,
16
I
XTAL2
17
O
SOUT
11
O
GND
20
CTS
36
I
DSR
37
I
DTR
33
O
ACTIVE
LEVEL
DESCRIPTION
H
DATA IN STROBE, DATA IN STROBE: DISTR, DISTR are read inputs which cause
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the 82C50A to output data to the data bus (D0-D7). The data output depends upon
the register selected by the address inputs A0, A1, A2. The chip select inputs CS0,
CS1, CS2 enable the DISTR, DISTR inputs.
Only an active DISTR or DISTR, not both, is used to receive data from the 82C50A
during a read operation. If DISTR is used as the read input, DlSTR should be tied
high. If DISTR is used as the active read input, DISTR should be tied low.
H
DATA OUT STROBE, DATA OUT STROBE: DOSTR, DOSTR are write inputs which
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cause data from the data bus (D0-D7) to be input to the 82C50A. The data input de-
pends upon the register selected by the address inputs A0, A1, A2. The chip select
inputs CS0, CS1, CS2 enable the DOSTR, DOSTR inputs.
Only an active DOSTR or DOSTR, not both, is used to transmit data to the 82C50A
during a write operation. If DOSTR is used as the write input, DOSTR should be tied
high. If DOSTR is used as the write input, DOSTR should be tied low.
DATA BITS 0-7: The Data Bus provides eight, three-state input/output lines for the
transfer of data, control and status information between the 82C50A and the CPU.
For character formats of less than 8 bits, D7, D6 and D5 are “don’t cares” for data
write operations and 0 for data read operations. These lines are normally in a high
impedance state except during read operations. D0 is the Least Significant Bit (LSB)
and is the first serial data bit to be received or transmitted.
H
REGISTER SELECT: The address lines select the internal registers during CPU
bus operations. See Table 1.
CRYSTAL/CLOCK: Crystal connections for the internal Baud Rate Generator.
XTAL1 can also be used as an external clock input, in which case XTAL2 should be
left open.
SERIAL DATA OUTPUT: Serial data output from the 82C50A transmitter circuitry. A
Mark (1) is a logic one (high) and Space (0) is a logic zero (low). SOUT is held in the
Mark condition when the transmitter is disabled, MR is true, the Transmitter Register
is empty, or when in the Loop Mode. SOUT is not affected by the CTS input.
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GROUND: Power supply ground connection (V_SS).
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CLEAR TO SEND: The logical state of the CTS pin is reflected in the CTS bit of the
(MSR) Modem Status Register (CTS is bit 4 of the MSR, written MSR (4)). A change
of state in the CTS pin since the previous reading of the MSR causes the setting of
DCTS (MSR(O)) of the Modem Status Register. When CTS pin is ACTIVE (low), the
modem is indicating that data on SOUT can be transmitted on the communications
link. If CTS pin goes INACTIVE (high), the 82C50A should not be allowed to transmit
data out of SOUT. CTS pin does not affect Loop Mode operation.
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DATA SET READY: The logical state of the DSR pin is reflected in MSR(5) of the
Modem Status Register. DDSR (MSR(1)) indicates whether the DSR pin has
changed state since the previous reading of the MSR. When the DSR pin is ACTIVE
(low), the modem is indicating that it is ready to exchange data with the 82C50A,
while the DSR Pin INACTIVE (high) indicates that the modem is not ready for data
exchange. The ACTIVE condition indicates only the condition of the local Data Com-
munications Equipment (DCE), and does not imply that a data circuit as been estab-
lished with remote equipment.
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DATA TERMINAL READY: The DTR pin can be set (low) by writing a logic 1 to
MCR(0), Modem Control Register bit 0. This signal is cleared (high) by writing a logic
0 to the DTR bit (MCR(0)) or whenever a MR ACTIVE (high) is applied to the
82C50A. When ACTIVE (low), DTR pin indicates to the DCE that the 82C50A is
ready to receive data. In some instances, DTR pin is used as a power on indicator.
The INACTIVE (high) state causes the DCE to disconnect the modem from the tele-
communications circuit.
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