Enhanced Parallel Port - Computer Busses - page 289

HostClk

PeriphAck

D0-D7 First byte Second byte

HostAck Data Command

nReverse
Request

nAck
Reverse

Figure 17.8 ECP Reverse data and command cycle
The operation of the ECP port is similar to the EPP port. The ECR register is used to set an
operational mode, after which an I/O port is used to transfer data (the actual port depends on
the mode). Handshaking is done automatically by the hardware and there is no need for the
software to control it.

Table 17.6 ECR Register Modes

Mode Description Mode Description

000 SPP mode 100 EPP parallel port mode (note 1)

001 Bidirectional mode (byte

mode)

101 (reserved)

010 Fast Centronics 110 Test mode

011 ECP parallel port mode 111 Configuration mode

Table 17.7 ECP register description

Offset Name Read/Write ECP Mode Function

000 Data R/W 000-001 Data register

000 ecpAfifo R/W 011 ECP address FIFO

001 dsr R/W all Status register

002 dcr R/W all Control register

400 cFifo R/W 010 Parallel port data FIFO

400 ecpDfifo R/W 011 ECP data FIFO

400 tfifo R/W 110 Test FIFO

400 cnfgA R 111 Configuration register A

401 cnfgB R/W 111 Configuration register B

402 ecr R/W all Extended control register