MC68HC901 Datasheet, PDF (18/73 Pages) Motorola, Inc – Multi-Function Peripheral

Signal Description
2.10.2 Serial Output (SO)
This output line is the USART transmitter data output. This output is in a high-impedance
state after a device reset.
2.10.3 Receiver Clock (RC)
This input controls the serial bit rate of the receiver. The signal may be supplied by the timer
output lines or by an external TTL-level clock which meets the minimum and maximum cycle
times. This clock is not used in the USART loopback mode. Refer to Section 7.3.2
Transmitter Status Register for additional information.
2.10.4 Transmitter Clock (TC)
This input controls the serial bit rate of the transmitter. This signal may be supplied by the
timer output lines or by an external TTL-level clock which meets the minimum and maximum
cycle times.
2.11 DIRECT MEMORY ACCESS CONTROL
The USART section of the MFP supports direct memory access transfers through its
receiver ready and transmitter ready status lines.
2.11.1 Receiver Ready (RR)
This active low output reflects the receiver buffer full status (bit 7 in the Receiver Status
Register) for DMA operations.
2.11.2 Transmitter Ready (TR)
This active low output reflects the transmitter buffer empty (bit 7 in the Transmitter Status
Register) for DMA operations.
2.12 SIGNAL SUMMARY
The following table is a summary of all the signals discussed in the previous paragraphs.
SIGNAL NAME
Power Input
Ground
Clock
Chip Select
Data Strobe
Read / Write
Table 2-1. Signal Summary
MNEMONIC
V_CC
GND
CLK
CS
DS
R/W
INPUT/
OUTPUT
Input
Input
Input
Input
Input
Input
ACTIVE
STATE
High
Low
N/A
Low
Low
Read – High,
Write – Low
THREE-
STATE
—
—
RESET
STATE
—
—
2-5
MC68HC901 USER’S MANUAL
MOTOROLA