DS89C420-QCL Datasheet, PDF (111/139 Pages) Maxim Integrated Products – Ultra-High-Speed Flash Microcontroller User’s Guide

Ultra-High-Speed Flash
Microcontroller User’s Guide
Table 11-5. Watchdog Timer-Related Bits
BIT NAMES
EWT
RWT
WD1,WD0
WTRF
EWDI
WDIF
DESCRIPTION
Enable watchdog timer reset
Reset watchdog timer
Watchdog interval control bits 1, 0
Watchdog timer reset flag
Enable watchdog timer interrupt
Watchdog interrupt flag
REGISTER LOCATION
WDCON – D8h
WDCON – D8h
CKCON – 8Eh
WDCON – D8h
EIE – E8h
WDCON – D8h
BIT POSITIONS
WDCON.1
WDCON.0
CKCON.7,6
WDCON.2
EIE.4
WDCON.3
Section 12: SERIAL I/O
The ultra-high-speed microcontroller provides two fully independent UARTs (serial ports) with framing-error detection and automatic
address recognition. The two UARTs can be operated simultaneously in identical or different modes and communication speeds. In
this documentation, all descriptions apply to both UARTs, unless stated otherwise.
Each serial port is capable of both synchronous and asynchronous modes. In the synchronous mode, the microcontroller generates
the clock and operates the UART in a half-duplex mode. In the asynchronous mode, full-duplex operation is available. Receive data is
buffered in a holding register. This allows the UART to receive an incoming word before software has read the previous value. Each
UART has an associated control register (SCON0, SCON1) and each has a transmit/receive register (SBUF0, SBUF1). The SFR loca-
tions are: SCON0, 98h; SBUF0, 99h; SCON1, C0h; SBUF1, C1h. The SBUF location provides access to both transmit and receive reg-
isters. Reads are directed to the receive buffer and writes to the transmit buffer automatically.
SERIAL MODE SUMMARY
Each port provides four operating modes. These offer different communication protocols and baud rates.
The four serial operating modes and max baud rate for each are shown in Table 12-1, followed by a brief summary of each mode.
Detailed descriptions of the modes are provided later in this section. In addition, provisions for use of the serial ports in conjunction
with the crystal multiplier and power-management mode are discussed later in this section.
MODE 0
Mode 0 provides synchronous communication with external devices. It is commonly used to communicate with serial peripherals. Serial
I/O occurs on the RXD pin. The shift clock is provided on the TXD pin. Note that, whether transmitting or receiving, the serial clock is
generated by the ultra-high-speed microcontroller. Thus, any device on the serial port in mode 0 must accept the microcontroller as
the master.
When not using power-management mode, the baud rate in mode 0 is the system clock frequency divided by either 12 or 4, as select-
ed by the SM2 bit for the associated UART. When set to a logic 0, the serial port runs at a divide-by-12. When set to a logic 1, the ser-
ial port runs at a divide-by-4. The SM2 bit for serial port 0 is located at SCON0.5 and the SM2 bit for serial port 1 is located at SCON1.5.
With the exception of the additional new divide-by-4 selection (supported by SM2), mode 0 operation is identical to the 80C32.
Table 12-1. Serial I/O Modes and Max Baud Rates
MODE
0
1
2
3
SYNC/
ASYNC
Sync
Async
Async
Async
BAUD CLOCK^†
4 or 12 tCLK
Timer 1 or 2*
32 or 64 tCLK
Timer 1 or 2*
START/STOP
None
1 start, 1 stop
1 start, 1 stop
1 start, 1 stop
†Use _{of the crystal multiplier or power-management mode affects the baud clock.}
*Timer 2 available for serial port 0 only.
DATA BITS
8
8
9
9
9TH BIT
FUNCTION
None
None
0, 1, parity
0, 1, parity
MAX BAUD RATE
SYSCLK = 33MHz
8,250,000
2,062,500
1,031,250
2,062,500
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