IA186EM/IA188EM
Data Sheet
8-Bit/16-Bit Microcontrollers
February 25, 2011
2.2.33 s2_n–s0_n—Bus Cycle Status (synchronous outputs with tristate)
These three signals inform the system of the type of bus cycle in progress. The s2_n may be
used to indicate whether the current access is to memory or I/O, and s1_n may be used to
indicate whether data is being transmitted or received. These signals are tristated during bus
hold and hold acknowledge. The coding for these pins is presented in Table 10.
Table 10. Bus Cycle Types for s2_n, s1_n, and s0_n
s2_n s1_n s0_n Bus Cycle
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Interrupt acknowledge
Read data from I/O
Write data to I/O
Halt
Instruction fetch
Read data from memory
Write data to memory
None (passive)
2.2.34 s6/clkdiv2_n/pio29—Bus Cycle Status Bit 6 (synchronous output)/Clock Divide
by 2 (input with internal pull-up)
The s6 signal is high during the second and remaining cycle periods (i.e., t2 – t4), indicating that a
DMA-initiated bus cycle is underway. The s6 is tristated during bus hold or reset.
If the clkdiv2_n signal is held low during power-on-reset, the microcontroller enters clock
divide-by-2 mode. In this mode, the PLL is disabled and the processor receives the external
clock divided by 2. Sampling of this pin occurs on the rising edge of res_n.
Note: If this pin is used as pio29 and configured as an input, care should be
taken that it is not driven low during POR.
Because this pin has an internal pull-up, it is not necessary to drive the pin high even though it
defaults to an input PIO.
2.2.35 sclk—Serial Clock (synchronous outputs with tristate)
Because this pin provides a slave device with a synchronous serial clock it permits
synchronization of the transmit and receive data exchanges between the slave and the
microcontroller. The sclk is the result of dividing the internal clock by 2, 4, 8, or 16, depending
on the contents of the Synchronous Serial Control (SSC) register Bits [5–4]. Accessing either
the SSR or SSD registers activates the sclk for eight cycles. When sclk is not active, the
microcontroller hold is high.
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