Zilog Z16C30 - Manual (Page 165)

8-10
Z16C30 USC ®
U SER ' S M ANUAL Z ILOG
UM97USC0100
8.8 REGISTER REFERENCE
The following pages include all of the fields in all of the
registers in one of the USC’s channels, plus the Bus
Configuration Register which is common to both channels.
They are arranged in alphabetical order by register name,
like Table 2 in Chapter 2. (If you want to look up a register
by its address/register number, look in Table 1 in Chapter
2 and then come back here)
8.8.1 Register Addresses
These are located to the right of the name of each register
on the following pages, and are shown as d b aaaaa,
where:
d represents the state of D//C (1=high=data)
b is 1 for a byte access on a 16-bit bus (it’s just
shown as “b” in all cases, like a placeholder);
aaaaa is the actual register address, from AD5-1, AD13-
9, or CCAR5-1.
8.8.2 Conditions/Context
Entries in this column indicate the conditions under which
descriptions to their right apply or can validly be used. If an
entry is blank, the description to the right always applies.
8.8.3 Description
Often entries in this column consist of one or more suben-
tries of the form “value=description”. If some possible
values aren’t shown, it may mean they are reserved (and
should not be written) or that they will never be read. Or,
particularly for single Read-Write bits, if the other case is
obvious, it’s left out. For example, for an entry like “1=dog
is dead” we didn’t feel obliged to add “0=dog is alive”. The
following abbreviation is used in some entries in this
column and “Conditions/Context”:
:= this “assignment operator” indicates that the value
on its right is written to the field or bit on its left.
8.8.4 RW Status
This column includes the following codes for each register
field:
RW The field is fully under the control of software,
and can be read and written.
RO The field is read only; writing to it has no effect.
ROC The bit is read-only; the USC clears it automati-
cally after software reads it as 1.
WO The field is write-only; reading it will either
return zeroes or an unrelated item that’s de-
scribed next in the list.
WOC The field is write only. After using its value the
USC will clear it to zero, so that it points back
to the indirect address register.
R,W1C The bit is set by the USC hardware, writing a 1
to it clears it.
R,W1U The bit is controlled by the USC hardware,
writing a 1 to it “unlatches” it.
UM009402-0201