XR16C2850
SYMBOL DESCRIPTION
Symbol
Pin
44
Signal
type
Pin Description
40
48
XTAL1
16
18
13
I
Crystal or External Clock Input - Functions as a crystal input
or as an external clock input. A crystal can be connected
between this pin and XTAL2 to form an internal oscillator
circuit. This configuration requires an external 1 MW resis-
tor between the XTAL1 and XTAL2 pins. Alternatively, an
external clock can be connected to this pin to provide
custom data rates (see Baud Rate Generator Program-
ming).
XTAL2
17
19
14
O
I
Output of the Crystal Oscillator or Buffered Clock - (see also
XTAL1). Crystal oscillator output or buffered clock output.
Should be left open if an external clock is connected to
XTAL1.
-CD A-B
-CTS A-B
38,19 42,21 40,16
36,25 40,28 38,23
Carrier Detect (active low) - These inputs are associated
with individual UART channels A through B. A logic 0 on this
pin indicates that a carrier has been detected by the modem
for that channel.
I
CleartoSend(activelow)-Theseinputsareassociatedwith
individual UART channels, A through B. A logic 0 on the -
CTS pin indicates the modem or data set is ready to accept
transmitdatafromthe2850.Statuscanbetestedbyreading
MSR bit-4. This pin has no effect on the UARTs transmit or
receive operation.
-DSR A-B
-DTR A-B
37,22 41,25 39,20
33,34 37,38 34,35
I
Data Set Ready (active low) - These inputs are associated
with individual UART channels, A through B. A logic 0 on
this pin indicates the modem or data set is powered-on and
is ready for data exchange with the UART. This pin has no
effect on the UARTs transmit or receive operation.
O
Data Terminal Ready (active low) - These outputs are
associated with individual UART channels, A through B. A
logic 0 on this pin indicates that the 2850 is powered-on and
ready. This pin can be controlled via the modem control
register. Writing a logic 1 to MCR bit-0 will set the -DTR
outputtologic0, enablingthemodem. Thispinwillbealogic
1 after writing a logic 0 to MCR bit-0, or after a reset. This
Rev. 1.00P
6
EXAR [ EXAR CORPORATION ]
