Zilog Z80195 - Manual (Page 45)

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Z80185/195 D EVELOPMENT K IT
U SER ' S M ANUAL
UM951800100
Z ILOG
OVERVIEW (Continued)
P1284 Key Features
■ There are separate drivers for inclusion in printers (peripheral) and the host computer.
■ Both drivers support compatible, byte, nibble, and ECP modes.
■ Both drivers achieve high data rates by using the hardware support of the Z80185/195 for data
transfer. In most cases, performance will be limited by the "other end" of the P1284 cable.
■ P1284 mode used by the P1284 host driver is determined by software—when you open the 1284
printer driver, it will use any of the supported modes that the attached host requests.
■ When your software requests to transmit data, each driver will do all the signaling necessary to
set the P1284 connection to the outgoing direction and send the data.
■ When no data is available to be transmitted, each driver will "listen" for incoming data and send
it to your application.
■ The printer software can specify the device ID, and the P1284 printer driver will send it to the host
automatically whenever it is requested.
■ The host software can request the device ID of the attached printer, and the P1284 host driver
will fetch it.
Performance
In ECP mode, the burst transfer speed is limited only by the speed of the DMA channel and the speed
of the station at the other end of the 1284 connection. Two Z80185/195s operating at 18.432 MHz can
communicate in ECP mode at approximately 1.4 MBytes/sec., and even faster for higher clock rates.
In compatibility mode, the burst transfer speed is limited by the pulse widths required by the P1284
standards; two Z80185/195’s can achieve approximately 0.7 MBytes/sec. in this mode.