General-Purpose Bus Controller
13-20
Élan™SC520 Microcontroller User’s Manual
The latest assertion time for these two signals is the same as the timing for the GPRDY
deassertion time (see “GPRDY Recognition” on page 13-20).
Figure 13-15 shows the GPIOCS16
timing for a 16-bit access and an 8-bit access.
Figure 13-15 16-Bit Access of a 16-Bit I/O Device
13.5.9.8
Wait States
The ÉlanSC520 microcontroller provides two ways to insert wait states in a GP bus cycle.
■
The user can program the programmable interface timing registers to delay the timing
of GPIORD, GPMEMRD, GPIOWR, or GPMEMWR for the required number of wait state
cycles.
■
GPRDY can also be used to insert wait states dynamically on a cycle basis.
GPRDY can only be used to stretch GP bus cycles; it cannot be used to provide early
termination of the cycle. The control signals are always asserted for a minimum of the entire
period, as programmed in the timing control registers. Then, the additional delay can be
inserted by the deassertion of GPRDY.
Figure 13-16 shows the timing of GPRDY.
13.5.9.8.1
GPRDY Recognition
Assuming a 33.333-MHz crystal, the GPRDY pin must be deasserted a minimum of 45 ns
before the programmed deassertion of the command strobes and must have a minimum
deassertion (Low) width of 30 ns to insert a wait state into a GP bus cycle. Additional wait
states are inserted by extending the time in which the GPRDY pin is held deasserted. The
Table 13-8
Dynamic Bus Sizing Override of Programmed Data Width
GP Chip Select Data Width
(GPCSDW)
Register Setting
GPIOCS16
GPMEMCS16 Assertion
Resultant Bus Size
8-bit
Deasserted
8-bit
8-bit
Asserted
16-bit
16-bit
Deasserted
16-bit
16-bit
Asserted
16-bit
Addr
Write Data
GPA23–GPA0,
GPCSx
GPIOCS16
GPD15–GPD0
Read Data
GPD15–GPD0
GPMEMRD, GPMEMWR,
GPIORD, or GPIOWR
GPBHE
Содержание Elan SC520
Страница 1: ...lan SC520 Microcontroller User s Manual Order 22004A...
Страница 4: ...iv lan SC520 Microcontroller User s Manual...
Страница 28: ...Introduction xxviii lan SC520 Microcontroller User s Manual...
Страница 42: ...Architectural Overview 1 14 lan SC520 Microcontroller User s Manual...
Страница 78: ...System Initialization 3 22 lan SC520 Microcontroller User s Manual...
Страница 108: ...Clock Generation and Control 5 10 lan SC520 Microcontroller User s Manual...
Страница 118: ...Reset Generation 6 10 lan SC520 Microcontroller User s Manual...
Страница 148: ...System Arbitration 8 24 lan SC520 Microcontroller User s Manual...
Страница 214: ...SDRAM Controller 10 36 lan SC520 Microcontroller User s Manual...
Страница 230: ...Write Buffer and Read Buffer 11 16 lan SC520 Microcontroller User s Manual...
Страница 288: ...GP Bus DMA Controller 14 22 lan SC520 Microcontroller User s Manual...
Страница 316: ...Programmable Interval Timer 16 8 lan SC520 Microcontroller User s Manual...
Страница 328: ...Software Timer 18 4 lan SC520 Microcontroller User s Manual...
Страница 346: ...Real Time Clock 20 12 lan SC520 Microcontroller User s Manual...
Страница 360: ...UART Serial Ports 21 14 lan SC520 Microcontroller User s Manual...
Страница 414: ...AMDebug Technology 26 8 lan SC520 Microcontroller User s Manual...