
SMSC DS – LPC47M14X 
Page 83 
Rev. 03/19/2001 
EPP 1.7 Read
The timing for a read operation (data) is shown in timing diagram EPP 1.7 Read Data cycle. The chip inserts wait states 
into the I/O read cycle when nWAIT is active low during the EPP cycle.  This can be used to extend the cycle time.  The 
read cycle can complete when nWAIT is inactive high. 
Read Sequence of Operation 
1) The host sets PDIR bit in the control register to a logic "1".  This deasserts nWRITE and tri-states the PData 
bus.   
2) The host initiates an I/O read cycle to the selected EPP register. 
3) Chip asserts nDATASTB or nADDRSTRB indicating that PData bus is tri-stated, PDIR is set and the nWRITE 
signal is valid. 
4) If nWAIT is asserted, the chip inserts wait states into the I/O read cycle until the peripheral deasserts nWAIT or 
a time-out occurs. 
5) The Peripheral drives PData bus valid. 
6) The Peripheral deasserts nWAIT, indicating that PData is valid and the chip may begin the termination phase 
of the cycle. 
7)   The chip drives the final sync and deasserts nDATASTB or nADDRSTRB. 
8) Peripheral tri-states the PData bus. 
9) Chip may modify nWRITE, PDIR and nPDATA in preparation of the next cycle. 
Table 41  –  EPP Pin Descriptions 
EPP 
SIGNAL 
EPP NAME 
TYPE 
EPP DESCRIPTION 
nWRITE 
nWrite 
O 
This signal is active low.  It denotes a write operation. 
PD<0:7> 
Address/Data 
I/O 
Bi-directional EPP byte wide address and data bus. 
INTR 
Interrupt 
I 
This signal is active high and positive edge triggered.  (Pass 
through with no inversion, Same as SPP). 
nWAIT 
nWait 
I 
This signal is active low.   It is driven inactive as a positive 
acknowledgement from the device that the transfer of data is 
completed.  It is driven active as an indication that the device is 
ready for the next transfer. 
nDATASTB 
nData Strobe 
O 
This signal is active low.   It is used to denote data read or write 
operation. 
nRESET 
nReset 
O 
This signal is active low.   When driven active, the EPP device 
is reset to its initial operational mode. 
nADDRSTB 
Address 
Strobe 
O 
This signal is active low.   It is used to denote address read or 
write operation. 
PE 
Paper End 
I 
Same as SPP mode. 
SLCT 
Printer 
Selected 
Status 
I 
Same as SPP mode. 
nERR 
Error 
I 
Same as SPP mode. 
Note 1:
 SPP and EPP can use 1 common register. 
Note 2:
 nWrite is the only EPP output that can be over-ridden by SPP control port during an EPP cycle.  For correct 
EPP read cycles, PCD is required to be a low.