User`s manual

54 PCL-848AB User's Manual
5.2. Transfer Speed
The data transfer speed is determined by several factors:
1) The instruction execution speed of the computers. (4.77 MBz PC/XT to 16 MHz
PC/AT to ?)
2) The software overhead.
3) The interface chip operating speed.
4) The clock rate of the DMA chip. (3 to 8 MBz)
5) DMA operating mode.
6) The operating speed of other processors that may be occupying the data bus. (e.g.
8087 coprocessor)
7) The speed of handshake of the peripheral devices.
8) The IEEE-488 cable length and capacitance.
Factors l), 4), and 6) are the nature of the PC. Factors 7) and 8) are determined by
your choice of devices and cables. For factor 5), you can choose block-transfer mode
DMA to get maximum speed with the risk that the PC may be hung. For factor 2), the
interface driver routine is written with a lot of effort to maximize execution speed by
handling the overhead effectively. For factor 3), the NEC7210 was chosen because it is
an interface chip that can operate handshaking with 2 speeds. The user can choose an
appropriate speed according to the actual situation by setting bit 12 of <SETTING%>
when calling INIT routine. This setting will change the handshake timing T1, T6, T7
and T9.
Bit 12 Speed : O Slow
1 Fast