Z86E04 Datasheet, PDF (26/44 Pages) Zilog, Inc. – CMOS Z8 OTP MICROCONTROLLERS

Z86E04/E08
CMOS Z8 OTP Microcontrollers
FUNCTIONAL DESCRIPTION (Continued)
The Z8 instructions can access registers directly or indi-
rectly through an 8-bit address field. This allows short 4-bit
register addressing using the Register Pointer.
In the 4-bit mode, the register file is divided into eight work-
ing register groups, each occupying 16 continuous loca-
tions. The Register Pointer (Figure 13) addresses the
starting location of the active working-register group.
r7 r6 r5 r4
r3 r2 r1 r0
R253
(Register Pointer)
The upper nibble of the register file address
provided by the register pointer specifies
the active working-register group.
FF
Register Group F
F0
R15 to R0
7F
70
6F
60
5F
50
4F
40
3F
Specified Working
30
Register Group
2F
20
1F
Register Group 1
10
0F
Register Group 0
The lower nibble
of the register
file address
provided by the
instruction points
to the specified
register.
R15 to R0
R15 to R4*
I/O Ports
00
R3 to R0
*Expanded Register Group (0) is selected in this figure
by handling bits D3 to D0 as "0" in Register R253(RP).
Zilog
Stack Pointer. The Z8 has an 8-bit Stack Pointer (R255)
used for the internal stack that resides within the 124 gen-
eral-purpose registers.
General-Purpose Registers (GPR). These registers are
undefined after the device is powered up. The registers
keep their last value after any reset, as long as the reset
occurs in the V_CC voltage-specified operating range. Note:
Register R254 has been designated as a general-purpose
register and is set to 00 Hex after any reset or Stop-Mode
Recovery.
Counter/Timer. There are two 8-bit programmable
counter/timers (T0 and T1), each driven by its own 6-bit
programmable prescaler. The T1 prescaler is driven by in-
ternal or external clock sources; however, the T0 can be
driven by the internal clock source only (Figure 14).
The 6-bit prescalers divide the input frequency of the clock
source by any integer number from 1 to 64. Each prescaler
drives its counter, which decrements the value (1 to 256)
that has been loaded into the counter. When both counter
and prescaler reach the end of count, a timer interrupt re-
quest IRQ4 (T0) or IRQ5 (T1) is generated.
The counter can be programmed to start, stop, restart to
continue, or restart from the initial value. The counters are
also programmed to stop upon reaching zero (Single-Pass
Mode) or to automatically reload the initial value and con-
tinue counting (Modulo-N Continuous Mode).
The counters, but not the prescalers, are read at any time
without disturbing their value or count mode. The clock
source for T1 is user-definable and is either the internal mi-
croprocessor clock divided by four, or an external signal in-
put through Port 3. The Timer Mode register configures the
external timer input (P31) as an external clock, a trigger in-
put that is retriggerable or non-retriggerable, or used as a
gate input for the internal clock.
Figure 13. Register Pointer
26
PRELIMINARY
DS97Z8X1104