Z86E30/E31/E40
Z8 4K OTP Microcontroller
Zilog
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
Counter/Timers. 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 prescaler
is driven by the internal clock only (Figure 27).
occurs in the V voltage-specified operating range. The
1
CC
register R254 is general-purpose on Z86E30/E31. R254
and R255 are set to 00H after any reset or STOP-Mode re-
covery.
The 6-bit prescalers can 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 the
counter reaches the end of count, a timer interrupt request,
IRQ4 (T0) or IRQ5 (T1), is generated.
RAM Protect. The upper portion of the RAM's address
spaces 80H to EFH (excluding the control registers) can
be protected from reading and writing. This option can be
selected during the EPROM Programming Mode. After this
option is selected, the user can activate this feature from
the internal EPROM. D6 of the IMR control register (R251)
is used to turn off/on the RAM protect by loading a 0 or 1,
respectively. A 1 in D6 indicates RAM Protect enabled.
RAM Protect is not available on the Z86E31.
Stack. The Z86E40 external data memory or the internal
register file can be used for the stack. The 16-bit Stack
Pointer (R254-R255) is used for the external stack, which
can reside anywhere in the data memory for ROMless
mode, but only from 4096 to 65535 in ROM mode. An 8-bit
Stack Pointer (R255) is used for the internal stack on the
Z86E30/E31/E40 that resides within the 236 general-pur-
pose registers (R4-R239). SPH (R254) can be used as a
general-purpose register when using internal stack only.
R254 and R255 are set to 00H after any reset or STOP-
Mode Recovery.
DS97Z8X0500
P R E L I M I N A R Y
37
ZILOG [ ZILOG, INC. ]
