cop888eb National Semiconductor Corporation, cop888eb Datasheet - Page 57

• Manufacturer Part Number: cop888eb
• Description: 8-bit Cmos Rom Based Microcontrollers With 8k Memory, Can Interface, 8-bit A/d, And Usart
• Manufacturer: National Semiconductor Corporation

USART
USART CONTROL AND STATUS REGISTERS
The operation of the USART is programmed through three
registers: ENU, ENUR and ENUI.
DESCRIPTION OF USART REGISTER BITS
ENU-USART Control and Status Register (Address at
0BA)
PEN: This bit enables/disables Parity (7- and 8-bit modes
only). Read/Write, cleared on reset.
PEN = 0
PEN = 1
PSEL1, PSEL0: Parity select bits. Read/Write, cleared on
reset.
PSEL1 = 0, PSEL0 = 0
PSEL1 = 0, PSEL0 = 1
PSEL1 = 1, PSEL0 = 0
PSEL1 = 1, PSEL0 = 1
XBIT9/PSEL0: Programs the ninth bit for transmission when
the USART is operating with nine data bits per frame. For
seven or eight data bits per frame, this bit in conjunction with
PSEL1 selects parity. Read/Write, cleared on reset.
CHL1, CHL0: These bits select the character frame format.
Parity is not included and is generated/verified by hardware.
Read/Write, cleared on reset.
CHL1 = 0, CHL0 = 0
CHL1 = 0, CHL0 = 1
CHL1 = 1, CHL0 = 0
CHL1 = 1, CHL0 = 1
ERR: This bit is a global USART error flag which gets set if
any or a combination of the errors (DOE, FE, PE) occur.
Read only; it cannot be written by software, cleared on reset.
RBFL: This bit is set when the USART has received a com-
plete character and has copied it into the RBUF register. It is
automatically reset when software reads the character from
RBUF. Read only; it cannot be written by software, cleared
on reset.
TBMT: This bit is set when the USART transfers a byte of
data from the TBUF register into the TSFT register for trans-
mission. It is automatically reset when software writes into
the TBUF register. Read only, bit is set to “one” on reset; it
cannot be written by software.
ENUR-USART Receive Control and Status Register
(Address at 0BB)
Note 33: Bit is reserved for future use. User must set to zero.
DOE: Flags a Data Overrun Error. Read only, cleared on
read, cleared on reset.
Bit 7
DOE
Bit 7
PEN
FE
PSEL1 XBIT9/
Parity disabled.
Parity enabled.
PE
(Continued)
PSEL0
Reserved
CHL1
The frame contains eight data bits.
The frame contains seven data
bits.
The frame contains nine data bits.
Loopback Mode selected. Trans-
mitter output internally looped back
to receiver input. Nine bit framing
format is used.
Odd Parity (if Parity enabled)
Even Parity (if Parity enabled)
Mark(1) (if Parity enabled)
Space(0) (if Parity enabled)
RBIT9
CHL0
ATTN
ERR
XMTG
RBFL
RCVG
Bit 0
TBMT
Bit 0
57
DOE = 0
DOE = 1
FE: Flags a Framing Error. Read only, cleared on read,
cleared on reset.
FE = 0
FE = 1
PE: Flags a Parity Error. Read only, cleared on read, cleared
on reset.
PE = 0
PE = 1
SPARE: Reserved for future use. Read/Write, cleared on re-
set.
RBIT9: Contains the ninth data bit received when the US-
ART is operating with nine data bits per frame. Read only,
cleared on reset.
ATTN: ATTENTION Mode is enabled while this bit is set.
This bit is cleared automatically on receiving a character with
data bit nine set. Read/Write, cleared on reset.
XMTG: This bit is set to indicate that the USART is transmit-
ting. It gets reset at the end of the last frame (end of last Stop
bit). Read only, cleared on reset.
RCVG: This bit is set high whenever a framing error occurs
and goes low when RDX goes high. Read only, cleared on
reset.
ENUI-USART Interrupt and Clock Source Register
(Address at 0BC)
STP2: This bit programs the number of Stop bits to be trans-
mitted. Read/Write, cleared on reset.
STP2 = 0
STP2 = 1
STP78: This bit is set to program the last Stop bit to be 7/8th
of a bit in length. Read/Write, cleared on reset.
ETDX: TDX (USART Transmit Pin) is the alternate function
assigned to Port L pin L2; it is selected by setting ETDX bit.
To simulate line break generation, software should reset
ETDX bit and output logic zero to TDX pin through Port L
data and configuration registers. Read/Write, cleared on re-
set.
SSEL: USART mode select. Read/Write, cleared on reset.
SSEL = 0
SSEL = 1
XRCLK: This bit selects the clock source for the receiver
section. Read/Write, cleared on reset.
XRCLK = 0
XRCLK = 1
XTCLK: This bit selects the clock source for the transmitter
section. Read/Write, cleared on reset.
XTCLK = 0
XTCLK = 1
ERI: This bit enables/disables interrupt from the receiver
section. Read/Write, cleared on reset.
Bit 7
STP2
STP78
Indicates no Framing Error has been detected
since the last time the ENUR register was read.
Indicates the occurrence of a Framing Error.
Indicates no Parity Error has been detected since
the last time the ENUR register was read.
Indicates the occurrence of a Parity Error.
Indicates no Data Overrun Error has been de-
tected since the last time the ENUR register
was read.
Indicates the occurrence of a Data Overrun Er-
ror.
One Stop bit transmitted.
Two Stop bits transmitted.
Asynchronous Mode.
Synchronous Mode.
The clock source is selected through the
PSR and BAUD registers.
Signal on CKX (L1) pin is used as the clock.
The clock source is selected through the
PSR and BAUD registers.
Signal on CKX (L1) pin is used as the clock.
ETDX
SSEL XRCLK XTCLK
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ERI
ETI
Bit 0