AMD Am186 CC User Manual page 62

Table 3-7 Signal Descriptions (Continued)
Multiplexed
1
Signal Name
Signal(s)
DEN
[DS]
[PIO30]
DT/R [PIO29]
HLDA {CLKSEL1}
3-12
System Overview
Type Description
Data Strobe provides a signal where the write cycle timing is
identical to the read cycle timing. When used with other control
signals, [DS] provides an interface for 68K-type peripherals
without the need for additional system interface logic.
O When [DS] is asserted, addresses are valid. When [DS] is
asserted on writes, data is valid. When [DS] is asserted on reads,
data can be driven on the AD bus.
Following a reset, this pin is configured as DEN. The pin is then
configured by software to operate as [DS].
Data Transmit or Receive indicates which direction data should
flow through an external data-bus transceiver. When DT/R is
O asserted High, the microcontroller transmits data. When this pin
is deasserted Low, the microcontroller receives data. DT/R is
three-stated with a pullup during a bus-hold or reset condition.
Bus-Hold Acknowledge is asserted to indicate to an external
bus master that the microcontroller has relinquished control of
the local bus. When an external bus master requests control of
the local bus (by asserting HOLD), the microcontroller completes
the bus cycle in progress, then relinquishes control of the bus to
the external bus master by asserting HLDA and three-stating
A19–A0, AD15–AD0, S2–S0, and S6. The following are also
three-stated and have pullups: BHE, DEN, DT/R, LCS, MCS3–
MCS0, PCS7–PCS0, RD, UCS, WHB, WLB, and WR. ALE is
three-stated and has a pulldown.
O
When the external bus master has finished using the local bus,
it indicates this to the microcontroller by deasserting HOLD. The
microcontroller responds by deasserting HLDA.
If the microcontroller requires access to the bus (for example,
for refresh), the microcontroller deasserts HLDA before the
external bus master deasserts HOLD. The external bus master
must be able to deassert HOLD and allow the microcontroller
access to the bus. See the timing diagrams for bus hold in the
microcontroller data sheet.
Am186™CC/CH/CU Microcontrollers User's Manual