HD64570 Datasheet, PDF (68/469 Pages) Hitachi Semiconductor – Serial Communications Adaptor

Table 2.7 System Control Lines (cont)
Pin Number
Symbol
BUSY
CP-84
80
FP-88
7
CPU0,
CPU1
74, 73
88, 87
Input/
Output
Description
Input/
output
(Open
drain)
Bus busy: indicates that the bus is in use.
Slave mode
Input line. An external device
drives BUSY active low to
indicate that it is using the bus.
When the SCA requests the
bus after the HOLDA or
BUSACK input becomes
active, if BUSY is low (active),
the SCA waits until BUSY goes
high (inactive) before taking
control of the bus.
Master mode
The SCA drives this line active
low as long as it holds the bus.
When it finishes using the bus,
the SCA drives this line high
(inactive) and releases the bus
after which this line becomes
an input line.
Input
Note: Be sure to pull this line up to V_CC.
MPU select: Select the bus interface mode.
CPU1
0
1
0
1
CPU0
0
0
1
1
CPU Mode
Mode 0 (8086-system 16-bit
MPU mode)
Mode 1 (64180 mode)
Mode 2 (68000-system 16-bit
MPU mode I)
Mode 3 (68000-system 16-bit
MPU mode II)
Note: Do not change the mode when the SCA is turned on.
Rev. 0, 07/98, page 52 of 453