AM186 Datasheet, PDF (44/112 Pages) Advanced Micro Devices – High-Performance, 80C186- and 80C188-Compatible, 16-Bit Embedded Microcontrollers with RAM

Pseudo Static RAM (PSRAM) Support
Reading and Writing the PCB
The Am186ER and Am188ER microcontrollers support Code intended to execute on the Am188ER microcon-
the use of PSRAM devices in low memory chip-select troller should perform all writes to the PCB registers as
(LCS) space only. When PSRAM mode is enabled, the byte writes. These writes will transfer 16 bits of data to
timing for the LCS signal is modified by the chip-select the PCB Register even if an 8-bit register is named in
control unit to provide a CS precharge period during the instruction. For example, out dx, al results in
PS RA M ac c es s es. T he 50 - MHz ti m in g of th e the ax value being written to the port address in dx.
Am186ER and Am188ER microcontrollers is appropri- Reads to the PCB should be done as word reads. Code
ate to allow 70-ns PSRAM to run with one wait state. written in this manner will run correctly on the
PSRAM mode is enabled through a bit in the Low Mem- Am188ER and Am186ER microcontrollers.
ory Chip-Select (LMCS) Register. The PSRAM feature
is disabled on CPU reset.
Unaligned reads and writes to the PCB result in unpre-
dictable behavior on both the Am186ER and Am188ER
In addition to the LCS timing changes for PSRAM pre- microcontrollers.
charge, the PSRAM devices also require periodic re-
fresh of all internal row addresses to retain their data.
Although refresh of PSRAM can be accomplished sev-
eral ways, the Am186ER and Am188ER microcontrol-
For a complete description of all the registers in the
PCB, refer to the Am186ER and Am188ER Microcon-
trollers User’s Manual, order #21684.
lers implement auto refresh only.
The Am186ER and Am188ER microcontrollers gener-
ate RFSH, a refresh signal, to the PSRAM devices
when PSRAM mode is enabled. No refresh address is
required by the PSRAM when using the auto refresh
mechanism. The RFSH signal is multiplexed with the
T _{MCS3 signal pin. When PSRAM mode is enabled,}
MCS3 is not available for use as a chip-select signal.
The refresh control unit must be programmed before
F ^{accessing PSRAM in LCS space. The refresh counter}
in the Clock Prescaler (CDRAM) Register must be con-
figured with the required refresh interval value. The re-
fresh counter reload value in the CDRAM Register
should not be set to less than 18 (12h) in order to pro-
A ^{vide time for processor cycles between refreshes. The}
refresh address counter must be set to 000000h to pre-
vent the MCS3–MCS0 or PCS6–PCS0 chip selects
from asserting. UCS may randomly assert during a
PSRAM refresh.
R _{LCS is held High and the A bus is not used during re-}
fresh cycles. The LMCS Register must be configured to
external ready ignored (R2 = 1) with one wait state
(R1–R0 = 01b), and the PSRAM mode enable bit (SE)
must be set. The ending address of LCS space in the
D _{LMCS Register must also be programmed.}
CLOCK AND POWER MANAGEMENT
The clock and power management unit of the
Am186ER and Am188ER microcontrollers includes a
phase-locked loop (PLL) and a second programmable
system clock output (CLKOUTB).
Phase-Locked Loop (PLL)
In a traditional 80C186/80C188 design, the internal clock
frequency is half the frequency of the crystal. Because of
the internal PLL on the Am186ER and Am188ER micro-
controllers, the internal clock generated by both micro-
controllers can operate at up to four times the frequency
of the crystal. The Am186ER and Am188ER microcon-
trollers operate in the following modes:
n Divide by Two—Frequency of the system clock is
half the frequency of the crystal with PLL disabled.
n Times One—Frequency of the system clock will be
the same as the external crystal with PLL enabled.
n Times Four—Frequency of the system clock is four
times the frequency of the crystal with PLL enabled.
The default Times Four mode must be used for processor
frequencies above 40 MHz. The Divide by Two mode
should be used for frequencies below 16 MHz. The clock-
ing mode is selected using CLKSEL1 and CLKSEL2 on
reset. Table 8 provides the maximum and minimum fre-
PERIPHERAL CONTROL BLOCK (PCB)
quencies for X1, X2, and CLKOUTA according to clocking
The integrated peripherals of the Am186ER and
mode.
Am188ER microcontrollers are controlled by 16-bit
read/write registers. The peripheral registers are con-
tained within an internal 256-byte control block. The
registers are physically located in the peripheral de-
Table 8. Maximum and Minimum Clock
Frequencies
vices they control, but they are addressed as a single
256-byte block. Figure 9 on page 46 shows a map of
Mode
X1/X2 X1/X2 CLKOUTA CLKOUTA
Max
Min
Max
Min
these registers.
Divide by 2 40 MHz 30 MHz 20 MHz
15 MHz
Times 1 40 MHz 16 MHz 40 MHz
16 MHz
Times 4 12.5 MHz 4 MHz 50 MHz
16 MHz
44
Am186^TMER and Am188^TMER Microcontrollers Data Sheet