Motorola MVME172 - Manual (Page 262)

4-26 Computer Group Literature Center Web Site
IP2 Chip
4
Note When programming b_WIDTH1-b_WIDTH0 for either 8-
bits or 16-bits, a_WIDTH1-a_WIDTH0 must be
programmed for one of 8-bits or 16-bits. This applies
whether or not a_MEN is set. For example, if offset $19 is set
to the value $09, then offset $18 can be set to $04, $05, $08,
or $09, but not to $00, or $01. The same relationship also
pertains to IP_c and IP_d, i.e., when programming
d_WIDTH1-d_WIDTH0 for either 8-bits or 16-bits,
c_WIDTH1-c_WIDTH0 must be programmed for one of 8-
bits or 16-bits. This applies whether or not c_MEN is set.
RT1, RT0 The recovery timers determine the time that must expire
from the acknowledgment of an IndustryPack I/O, ID, or
Interrupt Acknowledge cycle until the IP2 chip asserts a
new I/O, ID, or Int SEL* to the same IndustryPack. This
may help with some devices on IndustryPacks that require
dead time between cycles. Each recovery timer’s counter
starts incrementing at the assertion of its IPACK* signal
and continues to increment until it matches the value
encoded from its two recovery timer control bits. When it
reaches that value, the recovery time has expired and a
new cycle can be generated to the IndustryPack. The
recovery timer counters are cleared at reset. The recovery
times encoded by the recovery timer control bits are
shown in the following table. When a double size
IndustryPack is used at ab and the I/O space for ab is
accessed in the double size address range, the RT bits for
a and b should be programmed identically. The same
pertains to the RT bits for c and d.
There are some restrictions for using recovery timers with
double size IndustryPacks. When using a double size
IndustryPack, programmed recovery times for back-to-
WIDTH1 WIDTH0 Memory Space Data Width
0 0 32 bits
0 1 8 bits
1 0 16 bits
1 1 Reserved