The serial port on the Serial Watchdog is designed to run with a 9-pin straight cable (supplied) to a standard PC com port. The serial.exe program can be used to issue commands to the watchdog, or PC software can manage the watchdog directly.
For the Serial Watchdog timers to be enabled, the cable must be connected and the DTR signal from the controlling device must be "ON". Without this signal the outlet is simply kept "ON" and the timers are disabled. A single byte command received on the serial port can enable or disable the watchdog timer or the DCD toggle timer. The byte format is described below under the DIRECT CONTROL heading. The RTS signal must also be "ON" to enable the Serial Watchdog to recognize the byte command. Once the byte is sent, RTS can be turned off. The SERIAL.EXE program can generate the byte command for managing the watchdog timer. The DTR signal is echoed back as DSR, the RTS signal is echoed back as CTS, and transmitted data is echoed back on the receive data line. DCD is directly managed by the Serial Watchdog for interrupt generation. Power On state for DCD is OFF. DCD is also turned off and remains each time the watchdog turns off outlet power until the interrupt timer is reprogrammed.
When the Serial Watchdog initially receives power, power to the outlets is delayed a few seconds. This is the normal function and not a problem or flaw in the Serial Watchdog. Once the watchdog timer is enabled and when it expires, the outlet power is turned off for a few seconds (4-7) and then restored. Both the watchdog and the DCD toggle timers are disabled on initial power-up and after any power-down-up cycle.
SERIAL.EXE
SERIAL[.exe] watchdog command structure:
serial [port] [cnt@interval | OFF]
where:
port is COM1/COM2/COM3/COM4/hex_addr (default is COM1)
cnt is number of intervals (0=right now, 1=next occurence (may be short) to 15)
interval is one of:
.25 for 1/4 second interval counting
4 for 4 second interval counting
1 for 1 minute interval counting
16 for 16 minute interval counting
OFF (either case) indicates to turn off the watchdog timer
Examples:
serial off turn off the timer (connected on default COM1)
serial com2 12@.25 set timer for approximately 3 seconds
serial 2e8 4@16 set timer (com4:2e8) for 48-64 minutes
serial com1 0@4 power down-up right now
DIRECT CONTROL
Direct output through the serial port can also be achieved. For direct control use 19200 BPS, 8-bit, Non-parity with either 1 or 2 stop bits.
Traditional serial port definitions for PC usage (8250, 16450, 16550, 16650)
#define TXD 0 // transmit offset (when LCR x80 off)
#define RXD 0 // receive offset (when LCR x80 off)
#define RLO 0 // divisor of rate (low byte) (when LCR x80 on)
#define RHI 1 // divisor of rate (high byte)(when LCR x80 on)
#define IER 1 // interrupt enable register
#define IIR 2 // interrupt identification register
#define LCR 3 // line control register
#define MCR 4 // modem control register
#define LSR 5 // line status register
#define MSR 6 // modem status register
Traditional values of base are:
x3F8 for COM1
x2F8 for COM2
x3E8 for COM3
x2E8 for COM4
Program the port for 19200 BPS:
outb(base+LCR, 0x83); // access rate info
outb(base+RLO, 0x06); // 19200 baud
outb(base+RHI, 0x00);
outb(base+LCR, 0x03); // turn off rate info access
outb(base+MCR, 0x0F); // turn on DTR, RTS
Output the command byte(s)
outb(base+TXD, command); // send command, where command is the result
// of 'OR'ing the following
// x80 timer selection:
// x80 write to DCD toggle timer
// x00 write to watchdog timer
// x60 frequencey selection:
// x00 is 1/4 second
// x20 is 4 second
// x40 is 1 minute interval
// x60 is 15 minute interval
// x10 enable/disable timer:
// x10 is enabled
// x00 is disabled
// x0F interval counter