82091AA Datasheet, PDF (94/204 Pages) Intel Corporation – ADVANCED INTEGRATED PERIPHERAL (AIP)

82091AA
ECP Mode (ECR 7 5 ^e011)
When ECR 7 5 ^e011 the parallel port operates in
ECP mode In ECP mode both data and commands
(addresses and RLE) are transferred using the paral-
lel port 16-byte FIFO This information can be either
written to or read from the FIFO using DMA or non-
DMA ISA Bus transfers The parallel port interface
transfers use an automatic handshake generated by
the 82091AA The host controls the transfer direc-
tion by programming the DIR bit in the PCON Reg-
ister
When the host is writing to the peripheral device
(forward direction) STROBE and BUSY provide
the automatic handshake for transfer on the parallel
port interface (Figure 46) The peripheral device ne-
gates BUSY when it is ready to receive data or com-
mands AUTOFD indicates whether PD 7 0 con-
tain data (AUTOFD is high) or a command (AU-
TOFD is low) For commands (address or RLE)
the host writes to the ECPAFIFO Register I O ad-
dress and for data the host writes to the DFIFO
Register I O address The addresses and data are
placed in the same 16-byte FIFO When the FIFO is
full and cannot accept more data addresses the
FIFO Full status bit is set in the ECR
Data addresses written to the FIFO are transferred
to the peripheral device via PD 7 0 To begin a
transfer on the peripheral interface the 82091AA
checks BUSY to make sure the peripheral is in the
ready state If BUSY is negated the 82091AA drives
PD 7 0 and AUTOFD and asserts STROBE to
indicate that the data command is on PD 7 0 The
peripheral device asserts BUSY to indicate that it is
receiving the data command BUSY asserted caus-
es the 82091AA to negate STROBE
When the host is reading from the peripheral device
(reverse direction) AUTOFD and ACK provide
the automatic handshake for transfer on the parallel
port interface (Figure 47) Data commands from the
peripheral device are placed in the parallel port FIFO
using this handshake In this case BUSY indicates
whether PD 7 0 contain data (BUSY is high) or a
command (BUSY is low)
The peripheral device asserts ACK to indicate that
a data command is on PD 7 0 The 82091AA ne-
gates AUTOFD when it is ready for a peripheral
transfer and asserts AUTOFD to indicate that it is
receiving the data command AUTOFD asserted
causes the peripheral device to negate ACK The
peripheral transfers are to the parallel port 16-byte
FIFO
290486 – 46
Figure 46 ECP Mode Handshake (Forward Direction)
290486 – 47
Figure 47 ECP Mode Handshake (Reverse Direction)
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