cop87l88rg National Semiconductor Corporation, cop87l88rg Datasheet - Page 16

• Manufacturer Part Number: cop87l88rg
• Description: 8-bit One-time Programmable Microcontroller With Kbytes Program Memory
• Manufacturer: National Semiconductor Corporation

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UART
The device contains a full-duplex software programmable
UART The UART (Figure 12) consists of a transmit shift
register a receiver shift register and seven addressable reg-
isters as follows a transmit buffer register (TBUF) a receiv-
er buffer register (RBUF) a UART control and status regis-
ter (ENU) a UART receive control and status register
(ENUR) a UART interrupt and clock source register (ENUI)
a prescaler select register (PSR) and baud (BAUD) register
The ENU register contains flags for transmit and receive
functions this register also determines the length of the
data frame (7 8 or 9 bits) the value of the ninth bit in trans-
mission and parity selection bits The ENUR register flags
framing data overrun and parity errors while the UART is
receiving
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FIGURE 12 UART Block Diagram
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Other functions of the ENUR register include saving the
ninth bit received in the data frame enabling or disabling the
UART’s attention mode of operation and providing addition-
al receiver transmitter status information via RCVG and
XMTG bits The determination of an internal or external
clock source is done by the ENUI register as well as select-
ing the number of stop bits and enabling or disabling trans-
mit and receive interrupts A control flag in this register can
also select the UART mode of operation asynchronous or
synchronous
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