XA-S3 Datasheet, PDF (27/52 Pages) NXP Semiconductors – XA 16-bit microcontroller 32 K/1 K OTP/ROM/ROMless, 8-channel 8-bit A/D, low voltage 2.7 V.5.5 V, I2C, 2 UARTs, 16 MB address range

Philips Semiconductors
XA 16-bit microcontroller
32 K/1 K OTP/ROM/ROMless, 8-channel 8-bit A/D, low voltage (2.7 V–5.5 V),
I²C, 2 UARTs, 16 MB address range
Preliminary specification
XA-S3
INIT_WATCHDOG:
MOV CCAPM4, #4CH
; Module 4 in compare mode
MOV CCAP4L, #0FFH
; Write to low byte first
MOV CCAP4H, #0FFH
; Before PCA timer counts up to
; FFFF Hex, these compare values
; must be changed
OR CMOD, #40H
; Set the WDTE bit to enable the
; watchdog timer without changing
; the other bits in CMOD
;
;********************************************************************
;
; Main program goes here, but CALL WATCHDOG periodically.
;
;********************************************************************
;
WATCHDOG:
CLR EA
; Hold off interrupts
MOV CCAP4L, #00
; Next compare value is within
MOV CCAP4H, CH
; 255 counts of the current PCA
SETB EA
; timer value
RET
Figure 19. PCA Watchdog Timer Initialization Code
Watchdog Timer
This is a standard XA-G3 watchdog timer. This watchdog timer
always comes up running at reset. The watchdog acts the same on
EPROM, ROM, and ROMless parts, as in the XA-G3.
UARTs
Standard XA-S3 UART0 and UART1 with double buffered transmit
register. A flag has been added to SnSTAT that is set if any of the
status flags (BRn, FEn, or OEn) is set for the corresponding UART
channel. This allows polling for UART errors quickly at the interrupt
service routine. Baud rate sources may be timer 1 or timer 2.
The XA-S3 includes 2 UART ports that are compatible with the
enhanced UART used on the XA-G3.
The UART has separate interrupt vectors for each UART’s transmit
and receive functions. The UART transmitter has been double
buffered, allowing packed transmission of data with no gaps
between bytes and less critical interrupt service routine timing. A
break detect function has been added to the UART. This operates
independently of the UART itself and provides a start-of-break
status bit that the program may test. An Overrun Error flag allows
detection of missed characters in the received data stream. The
double buffered UART transmitter may require some software
changes if code is used that was written for the original XA-G3
single buffered UART.
Each UART baud rate is determined by either a fixed division of the
oscillator (in UART modes 0 and 2) or by the timer 1 or timer 2
overflow rate (in UART modes 1 and 3).
Timer 1 defaults to clock both UART0 and UART1. Timer 2 can be
programmed to clock either UART0 through T2CON (via bits R0CLK
and T0CLK) or UART1 through T2MOD (via bits R1CLK and
T1CLK). In this case, the UART not clocked by T2 could use T1 as
the clock source.
The serial port receive and transmit registers are both accessed at
Special Function Register SnBUF. Writing to SnBUF loads the
transmit register, and reading SnBUF accesses a physically
separate receive register.
The serial port can operate in 4 modes:
Mode 0: Serial I/O expansion mode. Serial data enters and exits
through RxDn. TxDn outputs the shift clock. 8 bits are
transmitted/received (LSB first). (The baud rate is fixed at 1/16 the
oscillator frequency.)
Mode 1: Standard 8-bit UART mode. 10 bits are transmitted
(through TxDn) or received (through RxDn): a start bit (0), 8 data
bits (LSB first), and a stop bit (1). On receive, the stop bit goes into
RB8 in Special Function Register SnCON. The baud rate is variable.
Mode 2: Fixed rate 9-bit UART mode. 11 bits are transmitted
(through TxD) or received (through RxD): start bit (0), 8 data bits
(LSB first), a programmable 9th data bit, and a stop bit (1). On
Transmit, the 9th data bit (TB8_n in SnCON) can be assigned the
value of 0 or 1. Or, for example, the parity bit (P, in the PSW) could
be moved into TB8_n. On receive, the 9th data bit goes into RB8_n
in Special Function Register SnCON, while the stop bit is ignored.
The baud rate is programmable to 1/32 of the oscillator frequency.
Mode 3: Standard 9-bit UART mode. 11 bits are transmitted
(through TxDn) or received (through RxDn): a start bit (0), 8 data
bits (LSB first), a programmable 9th data bit, and a stop bit (1).
In fact, Mode 3 is the same as Mode 2 in all respects except baud
rate. The baud rate in Mode 3 is variable.
In all four modes, transmission is initiated by any instruction that
uses SnBUF as a destination register. Reception is initiated in
Mode 0 by the condition RI_n = 0 and REN_n = 1. Reception is
initiated in the other modes by the incoming start bit if REN_n = 1.
2000 Dec 01
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