Parallel port signals

Pin	Signal mode names	Return pin	Signal source	Description: C = Compatibility mode; N = Nibble mode
1	Busy/PtrBusy	19	Printer	C mode: Positive true = not ready for data N mode: Data bits 3 then 7, then busy status
2	Select/Xflag	20	Printer	C mode: Positive true = online N mode: Data bits 1 then 5
3	nAck/PtrClk	21	Printer	C mode: Negative true = data transfer acknowledge N mode: Data qualifier
4	nFault/nDataAvail	22	Printer	C mode: Negative true = printer fault exists that prevents printing N mode: Negative low = data ready, then data bits 0 then 4
5	PError/AckDataReq	23	Printer	C mode: Positive true = printer error exists, such as media tray empty N mode: Data bits 2 then 6
6	Data 1	24	Host	C mode: Positive true data input N mode: Not used
7	Data 2	25	Host	C mode: Positive true data input N mode: Not used
8	Data 3	26	Host	C mode: Positive true data input N mode: Not used
9	Data 4	27	Host	C mode: Positive true data input N mode: Not used
10	Data 5	28	Host	C mode: Positive true data input N mode: Not used
11	Data 6	29	Host	C mode: Positive true data input N mode: Not used
12	Data 7	30	Host	C mode: Positive true data input N mode: Not used
13	Data 8	31	Host	C mode: Positive true data input N mode: Not used
14	nInit/nHostRTS	32	Host	C mode: Negative true = reset interface N mode: Set positive
15	nStrobe/HostClk	33	Host	C mode: Negative true = transfer data into printer input latch on rising edge N mode: Negative true = transfer Extensibility Request value into printer input latch on rising edge
16	nSelectIn/1284 Active	34	Host	C mode: Negative true = select printer N mode: Used in conjunction with HostBusy for 1284 hardware handshaking
17	nAutoFd/HostBusy	35	Host	C mode: Not used N mode: Used in conjunction with 1284 Active for 1284 hardware handshaking
18	Host Logic High		Host	Positive true = host signals valid Negative true = host signals invalid
36	Peripheral Logic High		Printer	Positive true = printer on Negative true = printer off