Datasheet

Chapter 14. UART Modules 14-9
Register Descriptions
14.3.4 Modem Control Register (MODCTL)
The modem control register (MODCTL), Figure 14-5, controls whether UART1 is in
UART mode or in one of three modem modes.
Table 14-5 describes MODCTL fields.
7 6543210
Field ACRB AWR DSL DTS1 SHDIR MODE
Reset 1000_0000
R/W R/W
Address MBAR + 0x202
Figure 14-5. Modem Control Register (MODCTL)
Table 14-5. Modem Control Register (MODCTL) Field Descriptions
Bits Name Description
7 ACRB AC ‘97 cold reset (active low).
0 The genera-purpose I/O used as the AC ‘97 cold reset output pin is active
1 The genera-purpose I/O used as the AC ‘97 cold reset output pin is inactive
6 AWR AC ‘97 warm reset (active high)
0 Warm reset is inactive, letting UART1’s R
TS output to function normally as the AC ‘97 frame
sync.
1 Forces a 1 on UART1’s R
TS output, which is used as the AC ‘97 frame sync.
5–4 DSL Channel select for DMA channels 2 and 3. The sources for the interrupt request lines that drive
DMA DREQ
[3:2] are selected by multiplexers in UART1, which are controlled by DSL.
00 DMA DREQ2
is driven by UART0 combined Tx/Rx interrupt
DMA DREQ3
is driven by UART1 combined Tx/Rx interrupt
01 DMA DREQ2
is driven by UART1 Rx interrupt
DMA DREQ3
is driven by UART1 Tx interrupt
10 same as 00
11 DMA DREQ2
is driven by UART1 Rx interrupt
DMA DREQ3
is driven by UART1 combined Tx/Rx interrupt. This combination is a by-product of
implementation and may not be useful.
When UART1 uses both DREQ
lines, DREQ3 and DREQ2 are driven by the Tx FIFO empty and Rx
FIFO full conditions, respectively. The Rx FIFO not-empty condition can be used instead of Rx FIFO
full by clearing UMR1n[6]. UART0 and UART1 have separate request lines to the interrupt
controller. Each is sourced from the combined Tx/Rx interrupt from the associated UART.
3 DTS1 Delay of time slot 1. Determines the starting point of the first bit of the first time slot of a new frame.
0 The rising edge of frame sync
1 One bit-clock cycle after the rising edge of frame sync
2 SHDIR Shift direction. For AC ‘97 this bit must be 0.
0 Samples/time slots are transferred msb first
1 Samples/time slots are transferred lsb first
1–0 MODE Mode select for UART1.
00 UART mode (default mode after hard reset). Changing from modem mode back to UART mode
by writing 00 to this field has the same effect on UART1 as a hard reset—all registers and
control logic are reset and the Tx and Rx FIFO pointers are reinitialized, effectively emptying the
FIFOs.
01 8-bit CODEC interface mode
10 16-bit CODEC interface mode
11 AC ‘97 mode