SC28L92 Philips Semiconductors, SC28L92 Datasheet - Page 20

• Manufacturer Part Number: SC28L92
• Description: 3.3V-5.0V Dual Universal Asynchronous Receiver/Transmitter DUART
• Manufacturer: Philips Semiconductors

1. The three MR registers are accessed via the MR Pointer and Commands 0x1n and 0xBn (where n = represents receiver and transmitter enable bits)
Philips Semiconductors
MR1A[4:3]or MR1B[4:3] to ‘11’ for Channels A and B, respectively.
In this mode of operation, a ‘master’ station transmits an address
character followed by data characters for the addressed ‘slave’
station. The slave stations, with receivers that are normally disabled,
examine the received data stream and ‘wakeup’ the CPU (by setting
RxRDY)only upon receipt of an address character. The CPU
compares the received address to its station address and enables
the receiver if it wishes to receive the subsequent data characters.
Upon receipt of another address character, the CPU may disable the
receiver to initiate the process again.
A transmitted character consists of a start bit, the programmed
number of data bits, and Address/Data (A/D) bit, and the
programmed number of stop bits. The polarity of the transmitted A/D
bit is selected by the CPU by programming bit MR1A[2]/MR1B[2].
MR1A[2]/MR1B[2] = 0 transmits a zero in the A/D bit position, which
identifies the corresponding data bits as data while
MR1A[2]/MR1B[2] = 1 transmits a one in the A/D bit position, which
identifies the corresponding data bits as an address. The CPU
should program the mode register prior to loading the corresponding
data bits into the TxFIFO.
In this mode, the receiver continuously looks at the received data
stream, whether it is enabled or disabled. If disabled, it sets the
RxRDY status bit and loads the character into the RxFIFO if the
received A/D bit is a one (address tag), but discards the received
character if the received A/D bit is a zero (data tag). If enabled, all
received characters are transferred to the CPU via the RxFIFO. In
either case, the data bits are loaded into the data FIFO while the
A/D bit is loaded into the status FIFO position normally used for
parity error (SRA[5] or SRB[5]). Framing error, overrun error, and
break detect operate normally whether or not the receive is enabled.
Table 1. SC28L92 register addressing READ (RDN = 0), WRITE (WRN = 0)
NOTE:
2000 Jan 21
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
3.3V–5.0V Dual Universal Asynchronous
Receiver/Transmitter (DUART)
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
0
1
0
1
Mode Register A (MR0A, MR1A, MR2A)
Status Register A (SRA)
Reserved
Rx Holding Register A (RxFIFOA)
Input Port Change Register (IPCR)
Interrupt Status Register (ISR)
Counter/Timer Upper (CTU)
Counter/Timer Lower (CTL)
Mode Register B (MR0B, MR1B, MR2B)
Status Register B (SRB)
Reserved
Rx Holding Register B (RxFIFOB)
Interrupt vector (68K mode)
Misc. register (Intel mode), IVR Motorola mode
Input Port (IPR)
Start Counter Command
Stop Counter Command
20
PROGRAMMING
The operation of the DUART is programmed by writing control words
into the appropriate registers. Operational feedback is provided via
status registers which can be read by the CPU. The addressing of
the registers is described in Table 1.
The contents of certain control registers are initialized to zero on
RESET. Care should be exercised if the contents of a register are
changed during operation, since certain changes may cause
operational problems.
For example, changing the number of bits per character while the
transmitter is active may cause the transmission of an incorrect
character. In general, the contents of the MR, the CSR, and the
OPCR should only be changed while the receiver(s) and
transmitter(s) are not enabled, and certain changes to the ACR
should only be made while the C/T is stopped.
Each channel has 3 mode registers (MR0, 1, 2) which control the
basic configuration of the channel. Access to these registers is
controlled by independent MR address pointers. These pointers are
set to 0 or 1 by MR control commands in the command register
“Miscellaneous Commands”. Each time the MR registers are
accessed the MR pointer increments, stopping at MR2. It remains
pointing to MR2 until set to 0 or 1 via the miscellaneous commands
of the command register. The pointer is set to 1 on reset for
compatibility with previous Philips Semiconductors UART software.
Mode, command, clock select, and status registers are duplicated
for each channel to provide total independent operation and control.
Refer to Table 2 for register bit descriptions. The reserved registers
at addresses H‘02’ and H‘0A’ should never be read during normal
operation since they are reserved for internal diagnostics.
Mode Register A (MR0A, MR1A, MR2A)
Clock Select Register A (CSRA)
Command Register A (CRA)
Tx Holding Register A (TxFIFOA)
Aux. Control Register (ACR)
Interrupt Mask Register (IMR)
C/T Upper Preset Register (CTPU)
C/T Lower Preset Register (CTPL)
Mode Register B (MR0B, MR1B, MR2B)
Clock Select Register B (CSRB)
Command Register B (CRB)
Tx Holding Register B (TxFIFOB)
Interrupt vector (68K mode)
Misc. register (Intel mode), IVR Motorola mode
Output Port Conf. Register (OPCR)
Set Output Port Bits Command (SOPR)
Reset output Port Bits Command (ROPR)
Product specification
SC28L92