B&B Electronics ATXWDT, ATRWDT manual Pinouts, Registers

The four bit latch values are also readable. Reading these bits is recommended to verify the presence and setup of the WDT. The BASIC command INP <WDTaddress> is used to read from the WDT. The top three bits are not used and can be masked out. In the ATRWDT the fifth bit is the reset flag. It will be a 1 when the ATRWDT resets the computer and a 0 if the computer has not been reset by the ATRWDT. This bit will be cleared if the computer is turned off or after the bit has been read. A small example program, written in QuickBASIC can be found in Appendix B.

Table 4. Registers

Write Register	Read Register
L0	L0
L1	L1
L2	L2
L3	L3
X	Reset Flag FOR ATR
	X FOR ATX
X	X
X	X
X	X

X = Don’t Care

Pinouts

Three pins of the male DB-9 connector are used for the WDT. Pins 4 and 7 are the external device reset relay contacts. These are non-polarized, normally open contacts, and pins 3 and 7 are for the normally closed.

Figure 2 is a schematic of the output portion of the WDT.

10 Documentation Number ATxWDT-1303

B&B Electronics Mfg Co – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 B&B Electronics Ltd – Westlink Comm. Pk – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445