
W83877ATF
Publication Release Date: April 1998
- 87 -
Version 0.51
4
.2.6 Bit Map of Parallel Port and EPP Registers
REGISTER
7
6
5
4
3
2
1
0
Data Port (R/W)
PD7
PD6
PD5
PD4
PD3
PD2
PD1
PD0
Status Buffer (Read)
BUSY
ACK
PE
SLCT
ERROR
SLIN
1
1
TMOUT
Control Swapper (Read)
1
1
1
IRQEN
INIT
AUTOFD
STROBE
Control Latch (Write)
1
1
DIR
IRQ
SLIN
INIT
PD2
AUTOFD
STROBE
PD1
EPP Address Port
(R/W)
PD7
PD6
PD5
PD4
PD3
PD0
EPP Data Port 0 (R/W)
PD7
PD6
PD5
PD4
PD3
PD2
PD1
PD0
EPP Data Port 1 (R/W)
PD7
PD6
PD5
PD4
PD3
PD2
PD1
PD0
EPP Data Port 2 (R/W)
PD7
PD6
PD5
PD4
PD3
PD2
PD1
PD0
EPP Data Port 3 (R/W)
PD7
PD6
PD5
PD4
PD3
PD2
PD1
PD0
4.2.7 EPP Pin Descriptions
EPP NAME
TYPE
EPP DESCRIPTION
nWrite
O
Denotes an address or data read or write operation.
PD<0:7>
I/O
Bi-directional EPP address and data bus.
Intr
I
Used by peripheral device to interrupt the host.
nWait
I
Inactive to acknowledge that data transfer is completed. Active to
indicate that the device is ready for the next transfer.
PE
I
Paper end; same as SPP mode.
Select
I
Printer selected status; same as SPP mode.
nDStrb
O
This signal is active low. It denotes a data read or write operation.
nError
I
Error; same as SPP mode.
nInits
O
This signal is active low. When it is active, the EPP device is reset to its
initial operating mode.
nAStrb
O
This signal is active low. It denotes an address read or write operation.
4.2.8 EPP Operation
When the EPP mode is selected in the configuration register, the standard and bi-directional modes
are also available. The PDx bus is in the standard or bi-directional mode when no EPP read, write, or
address cycle is currently being executed. In this condition all output signals are set by the SPP
Control Port and the direction is controlled by DIR of the Control Port.
A watchdog timer is required to prevent system lockup. The timer indicates that more than 10
μ
S
have elapsed from the start
of the EPP
cycle to the time
WAIT
is de-asserted. The current EPP cycle
is aborted when a time-out occurs. The time-out condition is indicated in Status bit 0.