Z80189 Datasheet, PDF (53/107 Pages) Zilog, Inc. – GENERAL-PURPOSE EMBEDDED CONTROLLERS

Zilog
PRELIMINARY
Z80189/Z8L189
GENERAL-PURPOSE EMBEDDED CONTROLLERS
Bit 7. Clock Divide Select. Bit 7 of the CCR allows the
programmer to set the internal clock to divide the external
clock by 2 if the bit is 0 and divide-by-one if the bit is 1.
Upon reset, this bit is set to 0 and the part is in
divide-by-two mode. Since the on-board oscillator is not
guaranteed to operate above 20 MHz, an external source
must be used to achieve the maximum 33 MHz operation
of the part, i.e., an external clock at 66 MHz with 50% duty
cycle.
If an external oscillator is used in divide-by-one mode, the
minimum pulse width requirement must be satisfied.
Bits 6 and 3. STANDBY/IDLE Enable. These two bits are
used for enabling/disabling the IDLE and STANDBY mode.
Setting D6, D3 to 0 and 1, respectively, enables the IDLE
mode. In the IDLE mode, the clock oscillator is kept
oscillating but the clock to the rest of the internal circuit,
including the CLKOUT, is stopped. The Z8S180 enters
IDLE mode after fetching the second opcode of a SLEEP
instruction, if the I/O STOP bit is set.
Setting D6, D3 to 1 and 0, respectively, enables the
STANDBY mode. In the STANDBY mode, the clock oscil-
lator is stopped completely. The Z8S180 enters STANDBY
after fetching the second opcode of a SLEEP instruction,
if the I/O STOP bit is set.
Setting D6, D3 to 1 and 1, respectively, enables the
STANDBY-QUICK RECOVERY mode. In this mode, its
operations are identical to STANDBY except that the clock
recovery is reduced to 64 clock cycles after the exit
conditions are gathered. Similarly, in STANDBY mode, the
Z8S180 enters STANDBY after fetching the second opcode
of a SLEEP instruction, if the I/O STOP bit is set.
Bit 5. BREXT. This bit controls the ability of the Z8S180 to
honor a bus request during STANDBY mode. If this bit is
set to 1 and the part is in STANDBY mode, a BUSREQ is
honored after the clock stabilization timer is timed out.
Bit 4. LNPHI. This bit controls the drive capability on the
PHI Clock output. If this bit is set to 1, the PHI Clock output
is reduced to 33% of its drive capability.
Bit 2. LNIO. This bit controls the drive capability of the
external I/O pins of the Z80189/Z80L189. When this bit is
set to 1, the output drive capability of the following pins is
reduced to 33% of the original drive capability:
- CKS
- TxAI
- RxS/CTS1 - CKA0/DREQ0
- TxS
- TxA0
- CKAI/TEND0 - /RTS0
Bit 1. LNCPUCTL. This bit controls the drive capability of
the CPU Control pins. When this bit is set to 1, the output
drive capability of the following pins is reduced to 33% of
the original drive capability:
- /BUSACK
- /RD
- /WR
- /M1
-E
- /MREQ
- /IORQ
- /RFSH
- /HALT
- /TEND1
- TEST
- STATUS
Bit 0. LNAD/DATA. This bit controls the drive capability of
the Address/Data bus output drivers. If this bit is set to 1,
the output drive capability of the Address and Data bus
output is reduced to 33% of its original drive capability.
DS971890301
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